EXHIBIT 10.1

SHAREHOLDER AGREEMENT

     This Shareholder Agreement, dated February 15, 2005 (this “Agreement”), by
and between GenCorp Inc., an Ohio corporation (the “Company”), and Steel
Partners II, L.P., a Delaware limited partnership (“Steel”), for itself and its
Affiliates (collectively, “Shareholder”).

RECITALS

     A. As of the date of this Agreement, Shareholder Beneficially Owns
3,973,100 shares (the “Owned Shares”) of Common Stock, par value $0.10 per
share, of the Company (the “Common Shares”).

     B. The Company and Shareholder desire to provide for certain agreements
with respect to the election of directors, the release of certain Claims, the
Common Shares Beneficially Owned by Shareholder and other matters.

     NOW, THEREFORE, in consideration of the covenants herein and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Company and Shareholder hereby agree as follows:

SECTION 1. DEFINITIONS

     1.1 Certain Definitions. In addition to any other terms defined in this
Agreement, for purposes of this Agreement, the following terms have the
following meanings when used herein with the initial capital letters:

                (a) “Affiliate” has the meaning ascribed thereto in Rule 12b-2
under the Exchange Act.

                (b) “Associate” has the meaning ascribed thereto in Rule 12b-2
under the Exchange Act.

                (c) “Beneficial Owner” and “Beneficially Own” are defined in
accordance with the term “beneficial ownership” as defined in Rule 13d-3 under
the Exchange Act, and a Person will also be deemed to be the Beneficial Owner
of, and to Beneficially Own, Common Shares that such Person or any Affiliate of
such Person has the right to acquire (whether such right is exercisable
immediately or only after the passage of time) pursuant to any agreement,
arrangement or understanding or upon the exercise of conversion rights, exchange
rights, warrants, options or otherwise.

                (d) “Board” means the Directors of the Company in their capacity
as such.

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                (e) “Claim” means any action, claim, complaint, right or cause
of action, debt, demand or suit of any kind or nature whatsoever, statutory,
equitable or legal, foreseen or unforeseen, known or unknown, matured or
unmatured.

                (f) “Exchange Act” means the Securities Exchange Act of 1934, as
amended, and the rules and regulations thereunder.

                (g) “Holding Period” means the period beginning on the date of
this Agreement and ending on February 15, 2007, provided, however, the Holding
Period will end on February 15, 2006 if Shareholder irrevocably waives its
rights under Section 2.2 hereof in writing on or prior to December 31, 2005
(such waiver, the “Holding Period Termination Notice”).

                (h) “Independent Director” means an individual (1) who qualifies
as an “independent director” of the Company under the rules of the New York
Stock Exchange, as such rules may be amended, supplemented or replaced from time
to time, and (2) who is not an Affiliate or an Associate of Shareholder.

                (i) “New Director” means an individual who qualifies as an
Independent Director and is a recognized corporate governance expert elected or
nominated for election by the Board based on the recommendation of the Board’s
nominating committee (the “Nominating Committee”) following consultation with
Steel.

                (j) “Observer” means Warren G. Lichtenstein or Jack L. Howard or
if both Messrs. Lichtenstein or Howard cease to serve as an Observer or to be
affiliated with the general partner of Steel (the “Steel GP”) for any reason,
any senior executive of the Steel GP designated by Shareholder and reasonably
acceptable to the Company after consultation with the Nominating Committee.

                (k) “Person” has the meaning given to such term in
Section 3(a)(9) of the Exchange Act, as supplemented by the rules and
regulations thereunder.

                (l) “2005 Annual Meeting” means the annual meeting of the
Company’s shareholders to be held during the 2005 calendar year, and the “2006
Annual Meeting” and “2007 Annual Meeting” mean the annual meetings of
shareholders of the Company in the consecutive calendar years.

SECTION 2. DIRECTORS; GOVERNANCE; SHAREHOLDER PROPOSALS

     2.1 New Director. The Company will seek in good faith to identify and cause
to be elected a New Director as promptly as reasonably practicable. In
connection therewith, Steel may nominate individuals for consideration by the
Nominating Committee, and the Company will consult in good faith with Steel
prior to the initial appointment of the New Director. If a New Director has not
been elected to the Board by June 30, 2005, then, notwithstanding any other
provision hereof (but subject to Section 7.10), upon notice from Shareholder
this Agreement will terminate.

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     2.2 Observer. (a) During the Holding Period, the Observer will (1) receive
copies of all notices and written information furnished to the Board at
substantially the same time they are so furnished, (2) be permitted to be
present at all meetings of the Board (whether by phone or in person), subject to
the Chairman of the Board’s (the “Chairman”) right to exclude the Observer from
being present at any executive session of the Board, any session in which the
chief executive officer is excused and at any session during which matters that
the Chairman determines in good faith that Shareholder has an interest that is
in addition to or different from the interests of the Company’s shareholders
generally, and (3) be reimbursed for all out-of-pocket expenses incurred in
attending any such meeting on the same basis as the Directors of the Company,
but not be entitled to Directors’ fees or other compensation in connection
therewith.

               (b) Shareholder (1) acknowledges that the U.S. securities laws
prohibit any person who has access to material nonpublic information from
trading while in possession of such information or providing that information to
others in certain circumstances, and agrees to comply with these requirements,
and (2) will maintain in strict confidence all nonpublic information it receives
whether by virtue of this Section 2.2 or otherwise; provided, however, that
nothing in this clause (2) will prohibit Shareholder from disclosing any such
information to its attorneys, accountants or financial or other advisors in
connection with its assessment of its investment in the Company. Shareholder
will cause all such Persons to maintain the confidentiality of information as if
they were direct parties hereto and be responsible for any failure by any such
Person to do so.

               (c) Shareholder hereby withdraws all of its prior proposals under
Rule 14a-8 under the Exchange Act, including without limitation Steel’s
November 2, 2004 shareholder proposals thereunder (the “11-2-04 Proposal”).

     2.3 Voting. At any meeting of shareholders at which directors are to be
elected during the Holding Period (including at the 2005 Annual Meeting and, if
applicable, the 2006 Annual Meeting), Shareholder shall take such action as may
be required so that all Common Shares Beneficially Owned by Shareholder as of
the record dates for such meetings are voted for the election of the slate of
nominees for election to the Board selected by a majority of the directors.

     2.4 Quorum. A representative or representatives of Shareholder will be
present, in person or by proxy, at any meeting of shareholders of the Company
during the Holding Period so that all Common Shares Beneficially Owned by
Shareholder may be counted for the purpose of determining the existence of a
quorum at such meeting.

     2.5 Governance Structures; Committees. During the Holding Period, (a) the
Company agrees to take such steps as are necessary to establish or designate a
committee comprised solely of Independent Directors, including the New Director,
to conduct an annual review of the Company’s governance structures, including
its constituent documents and the matters referenced in the 11-2-04 Proposal,
and (b) the

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number of directors will not exceed ten. The 2006 Annual Meeting and 2007 Annual
Meeting will be held no earlier than February 16th of the relevant year.

SECTION 3. RELEASES

     3.1 Company Release. The Company, on behalf of itself, its directors,
officers, employees, representatives and agents, (collectively, the “Company
Releasors”) does hereby, fully and forever, release and discharge Shareholder,
its partners, directors, officers, employees, attorneys, representatives and
agents (collectively, the “Shareholder Releasees”) from any and all Claims that
the Company Releasors have, may have or might claim to have against the
Shareholder Releasees through the date hereof.

     3.2 Shareholder Release. The Shareholder, on behalf of itself, its
partners, directors, officers, employees, representatives and agents,
(collectively, the “Shareholder Releasors”) does hereby, fully and forever,
release and discharge the Company, its directors, officers, employees,
attorneys, representatives and agents (collectively, the “Company Releasees”)
from any and all Claims that the Shareholder Releasors have, may have or might
claim to have against the Company Releasees through the date hereof.

     3.3 No Admission of Liability, Etc. The releases provided for herein are
given and received for the purpose of compromising disputed claims. The giving
and receiving of such releases are not, and may not be construed to be,
admissions of liability on the part of any Person but are made for the purpose
of terminating among the parties hereto all disputes and any other actions or
causes of action of every kind and nature, legal or equitable, relating to or
arising out of Steel’s letter to the Company dated November 11, 2004.
Notwithstanding any other provision hereof, the Company’s release in Section 3.1
does not constitute a release of, or otherwise effect, any claim by or on behalf
of any shareholder of the Company; provided that (a) the Company will not of its
own volition assist any shareholder in asserting any such claim, and (b)
Shareholder will not of its own volition assist any other Person in asserting
any claim against any Company Releasee.

SECTION 4. AGREEMENTS REGARDING VOTING AND SECURITIES

     During the Holding Period and for 10 calendar days thereafter:

     4.1 Acquisition of Securities. Shareholder may not (and may not enter into
any discussions or arrangements with any Person to), directly or indirectly,
acquire, or offer or propose to acquire, Beneficial Ownership of any Common
Shares or securities convertible into or exercisable or exchangeable for Common
Shares (“Convertible Securities”), in each case now or hereafter outstanding
(collectively, “Securities,” and all Securities Beneficially Owned by
Shareholder, including the Owned Shares, being referred to herein as “Restricted
Securities”), if the effect of such acquisition would be to increase the
aggregate Beneficial Ownership of Restricted Securities of Shareholder

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to 19.9% or more of the total number of Common Shares then outstanding (the
“Percentage Limitation”).

     4.2 Proxy Solicitations. Subject to Section 4.10, Shareholder may not (and
may not enter into any discussions or arrangements with any Person to), directly
or indirectly, solicit proxies or initiate, propose or become a “participant” in
a “solicitation” (as such terms are defined in Regulation 14A under the Exchange
Act) in opposition to any matter that has been recommended by a majority of the
directors of the Company or in favor of any matter that has not been approved by
a majority of the directors of the Company or seek to advise, encourage or
influence any Person with respect to the voting of Securities in such manner, or
initiate or encourage or attempt to encourage any Person to initiate, any
shareholder proposal relating to the Company.

     4.3 Group Participation. Subject to Section 4.10, Shareholder may not (and
may not enter into any discussions or arrangements with any Person to) form,
join or in any way participate in a group (within the meaning of
Section 13(d)(3) of the Exchange Act) with respect to any securities of the
Company, including for the purpose of acquiring, holding, voting or disposing of
Securities, except as otherwise required by this Agreement.

     4.4 Voting Trust or Arrangement. Shareholder may not deposit any Restricted
Securities in a voting trust or subject any Restricted Securities to any
arrangement or agreement with respect to the voting of such Restricted
Securities unless such voting trust, arrangements or agreements comply with and
are subject to the provisions of this Agreement.

     4.5 Shareholder List. Subject to Section 4.10, without the express prior
written approval of the Company, Shareholder may not, directly or indirectly,
seek, request or obtain, or assist any other Person in seeking, requesting or
obtaining, the stock ledger, any list of security holders of the Company or any
other books and records of the Company.

     4.6 Shareholder Meetings. Subject to Section 4.10, without the express
prior written approval of the Company, Shareholder will not, directly or
indirectly, call or seek to have called, or assist any other Person in calling
or seeking to call, any special meeting of the shareholders of the Company for
any reason or execute any written consent with respect to the Company’s
Securities.

     4.7 Other Transactions. Shareholder may not, no director or executive
officer of Shareholder may, and Shareholder will cause its other officers,
employees or agents (including investment bankers) not to, (i) induce or attempt
to induce or give encouragement to any Person, or enter into any serious
substantive discussions or negotiations with any Person, in furtherance of any
tender offer, merger or any other form of business acquisition or combination
transaction in which Securities would be acquired or (ii) make any public
announcement with respect to, or submit any proposal for, the acquisition of
Beneficial Ownership of any Securities if the effect of such acquisition would
be to cause the Beneficial Ownership of Shareholder to exceed the

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Percentage Limitation, or for or with respect to any extraordinary transaction
or merger, consolidation, sale of substantial assets or business combination
involving the Company or any of its Affiliates, whether or not any Persons other
than partners or members of Shareholder are involved and whether or not such
proposal might require the making of a public announcement by the Company
(“Business Combination”); provided, however, that nothing in this Section 4.7
will, or will be construed, directly or indirectly, to limit any rights of
Shareholder to offer, sell or otherwise dispose of shares of Restricted
Securities pursuant to any transaction effected in accordance with Section 4.8.
Subject to Section 4.10, Shareholder may not, no director or executive officer
of Shareholder may, and Shareholder will cause its other officers, employees or
agents (including investment bankers) not to, (x) without the prior written
consent of the Company signed by the Chairman or CEO, propose any individual for
election to the Board or submit any shareholder proposal to the Company,
(y) without the prior written consent of the Chairman or CEO, seek the removal
of any Director of the Company, or (z) otherwise act alone or in concert with
others to seek to control or influence the management or policies of the Company
or any of its Affiliates, including, without limitation, taking any action to
seek to obtain representation on the Board or the board of directors of any
Affiliate of the Company or to seek the removal of any director or a change in
the size of the Board or the board of directors of any Affiliate of the Company.
Subject to Section 4.10, Shareholder will not, directly or indirectly, enter
into any discussions or arrangements with any Person with respect to any of the
agreements set forth in this Section 4.7; provided, however, that (a) nothing
herein will prohibit Shareholder from making a proposal to the Board to enter
into a Business Combination that (1) is made confidentially and not publicly
disclosed, whether in a press release, SEC filing or otherwise, (2) is expressly
conditioned on the continuing maintenance of its confidentiality and is not
intended to, or made in circumstances in which it could reasonably be expected
to, result in its public disclosure by the Company, and (3) is subject to
approval by the Board, and (b) this Section 4.7 will terminate (i) on the date
of any public announcement by the Company that the Company is negotiating a
Business Combination with a third party to the date such negotiations cease, or
(ii) following the public announcement by the Company that it has entered into
an agreement for a Business Combination with a third party.

     4.8 Dispositions. (a) Except as otherwise permitted by this Agreement or
with the express prior written approval of the Company, Shareholder may not (and
may not enter into any discussions or arrangements with any Person to), directly
or indirectly, offer, sell, dispose of, transfer or hypothecate (“Transfer”) any
Restricted Securities other than a Permitted Transfer or in privately negotiated
transactions in which Restricted Securities are not Transferred to any other
Person or group who or which would immediately thereafter, to the actual
knowledge of Shareholder after reasonable inquiry, Beneficially Own more than 5%
of the total number of Common Shares then outstanding or in open market
transactions.

               (b) The term “Permitted Transfer” will mean and include any of
the following: (i) any Transfer to or through a nationally recognized
broker-dealer so long as there is no agreement, understanding or knowledge as to
the identity of the purchaser(s); (ii) any Transfer pursuant to a transaction
effected on the floor of the New

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York Stock Exchange or any other national exchange, Nasdaq, or any inter-dealer
quotation system in which Shareholder has no knowledge that the purchaser is a
person who, after giving effect to such Transfer, would beneficially own 5% or
more of the outstanding Common Shares; or (iii) any Transfer pursuant to a
tender or exchange offer.

     4.9 Amendment and Waiver. Shareholder may not (and may not enter into any
discussions or arrangements with any Person to), directly or indirectly, request
that the Company (or any of its officers, directors, representatives, trustees,
employees, attorneys, advisers, agents, Affiliates or associates) waive, amend
or modify in any material respect any restrictions contained in this Agreement
(or waive, amend or modify this Section 4.9), it being understood that no
request whatsoever may be made that (a) is disclosed, or is required to be
disclosed, by Shareholder to any Person or in any filing under the Exchange Act
(including, without limitation, under Section 13(d) thereof) or (b) the Company
might be required to publicly disclose.

     4.10 Permitted Activity. Nothing contained in this Agreement shall limit
Shareholder from taking any of the actions otherwise prohibited in Sections 4.2
or 4.5 of this Agreement in connection with any annual or special meeting of
shareholders scheduled to take place at any time following the expiration of the
Holding Period (including the 2006 Annual Meeting or 2007 Annual Meeting, as
applicable, if Shareholder has given the Holding Period Termination Notice by
December 31, 2005), including, without limitation, nominating directors
requesting a shareholder list and related information, or taking any other
action related to the solicitation of proxies or written consents or making any
public filings or announcements in furtherance thereof.

     4.11 Other Requirements. For the avoidance of doubt, the covenants in this
Agreement, including without limitation this Section 4, are not intended to be
and will not be interpreted as being an approval by the Board of any acquisition
of stock by Steel Partners or its Affiliates for purposes of any provision of
Ohio law.

SECTION 5. REPRESENTATIONS AND WARRANTIES OF THE COMPANY

     The Company represents and warrants to Shareholder as follows:

     5.1 Corporate Existence of, and Due Authorization and Execution by, the
Company. The Company is a corporation duly organized, validly existing and in
good standing under the laws of the State of Ohio, with full corporate power and
authority to execute and deliver this Agreement, to perform its obligations
hereunder, and to consummate the transactions contemplated hereby. This
Agreement and the consummation of the transactions contemplated hereby have been
duly authorized by all necessary corporate action of the Company. This Agreement
has been duly executed and delivered by the Company and constitutes a legal,
valid and binding obligation of the Company, enforceable against the Company in
accordance with its terms.

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     5.2 No Conflicts. The execution and delivery of this Agreement and the
consummation of the transactions contemplated hereby do not conflict with, or
result in any violation of or default under, any provision of the Amended
Articles of Incorporation or Amended Code of Regulations of the Company.

SECTION 6. REPRESENTATIONS AND WARRANTIES OF SHAREHOLDER

     Shareholder represents and warrants to the Company as follows:

     6.1 Existence of, and Due Authorization and Execution by, Shareholder.
Shareholder is a limited partnership duly organized, validly existing, and in
good standing under the laws of the State of Delaware, with full power and
authority to execute and deliver this Agreement, to perform its obligations
hereunder, and to consummate the transactions contemplated hereby. This
Agreement and the consummation of the transactions contemplated hereby have been
duly authorized by all necessary action of Shareholder. This Agreement has been
duly executed and delivered by Shareholder and constitutes a legal, valid and
binding obligation of Shareholder, enforceable against Shareholder in accordance
with its terms.

     6.2 No Conflicts. The execution and delivery of this Agreement and the
consummation of the transactions contemplated hereby do not conflict with, or
result in any violation of or default under, any provision of any partnership
agreement or other constituent documents of Shareholder or of any agreement or
instrument binding upon Shareholder.

     6.3 Beneficial Ownership of Common Shares. As of the date of this
Agreement, (a) Shareholder Beneficially Owns the Owned Shares and no other
Securities, and (b) to the actual knowledge of Shareholder, no Affiliate of
Shareholder Beneficially Owns any Securities.

SECTION 7. MISCELLANEOUS

     7.1 Specific Enforcement. The parties acknowledge that the Company would be
irreparably damaged in the event any provision of this Agreement were not
performed in accordance with its specific terms or were otherwise breached. It
is accordingly agreed that the Company will be entitled to an injunction or
injunctions to prevent breaches of this Agreement and to specifically enforce
this Agreement and the terms and provisions thereof in any action instituted in
any court of the United States or any state thereof having subject matter
jurisdiction, in addition to any other remedy to which the Company may be
entitled, at law or in equity.

     7.2 Modification; Waiver. (a) This Agreement may be modified in any manner
and at any time by written instrument executed by the parties and (b) any of the
terms, covenants and conditions of this Agreement may be waived at any time by
the party entitled to the benefit of such term, covenant or condition.

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     7.3 Notices. All notices, requests, demands, claims, and other
communications hereunder will be in writing and will be delivered by electronic
transmission:

         

  (a)   if to the Company, to:
 
       

      GenCorp Inc.

      Highway 50 and Aerojet Road

      Rancho Cordova, California 95670

      Facsimile: (916) 351-8665

      Attention: Mark A. Whitney, Vice President, Deputy General Counsel and
Assistant Secretary

      Email: mark.whitney@gencorp.com
 
       

      with a copy to:
 
       

      Jones Day

      222 East 41st Street

      New York, New York 10017

      Facsimile: (212) 755-7306

      Attention: Robert A. Profusek, Esq.

      Email: raprofusek@jonesday.com
 
       

  (b)   if to Shareholder, to:
 
       

      Steel Partners II, L.P.

      590 Madison Avenue

      32nd Floor

      New York, New York 10022

      Facsimile: (212) 758-5789

      Attention: Warren G. Lichtenstein

      Email: warren@steelpartners.com
 
       

      with a copy to:
 
       

      Olshan Grundman Frome Rosenzweig & Wolosky LLP

      Park Avenue Tower

      65 East 55th Street

      New York, New York 10022

      Facsimile: (212) 451-2222

      Attention: Steven Wolosky, Esq.

      Email: swolosky@olshanlaw.com

               (c) or, in each case, at such other address or to such other
Person as may be specified in writing to the other party.

               (d) Notwithstanding any other provision hereof, any Holding
Period Termination Notice will be operative for purposes of this Agreement only
if it is given in

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accordance with this Section and expressly states that it is effective when
delivered as herein provided.

     7.4 Parties in Interest; Assignment. This Agreement and all the provisions
hereof are binding upon and will inure to the benefit of the parties and their
respective successors and permitted assigns, but neither this Agreement nor any
of the rights, interests and obligations hereunder may be assigned or delegated
by either party without the prior written consent of the other party. Nothing in
this Agreement, whether expressed or implied, may be construed to give any
Person other than the parties any legal or equitable right, remedy or claim
under or in respect of this Agreement.

     7.5 Counterparts. This Agreement may be executed in one or more
counterparts, all of which will constitute one and the same instrument.

     7.6 Headings; References. The section headings of this Agreement are for
convenience of reference only and will not be deemed to alter or affect the
meaning or interpretation of any provisions hereof. Unless otherwise specified,
references to “Sections” are to Sections of this Agreement.

     7.7 Governing Law, Etc. This Agreement is governed by and construed in
accordance with the internal laws of the State of New York applicable to
contracts made and to be performed therein, without regard to the conflict of
laws principles. Each party submits to exclusive jurisdiction and venue of
federal or state courts in New York, New York and agrees not to institute
litigation in any other forums in respect of the interpretation or enforcement
of this Agreement (except for proceedings to obtain enforcement of an order of a
New York, New York federal or state court).

     7.8 Severability. If one or more of the provisions of this Agreement are
held by a court of competent jurisdiction to be invalid, void or unenforceable,
the remainder of the provisions of this Agreement will remain in full force and
effect.

     7.9 Press Release. Immediately following the execution and delivery of this
Agreement, the Company and Shareholder shall issue the joint press release
attached hereto as Schedule A (the “Press Release”). None of the parties hereto
will knowingly make any public statements (including in any filing with the
Securities and Exchange Commission or any other regulatory or governmental
agency, including any stock exchange) that are inconsistent in any material
respect with the statements in the Press Release issued pursuant to this Section
7.9. Following the date hereof, Shareholder shall not issue or cause the
publication of any press release or other public announcement with respect to
this Agreement, the Company, its management or the Board or the Company’s
business without prior written consent of the Company; provided, however, that
Shareholder may file an amendment to its Schedule 13D with respect to its
investment in the Company and either party may otherwise make such public
announcements as its counsel reasonably determines are required by law as a
result of a statement, fact or development that itself does not breach or
conflict with the terms of this Agreement so long as the other party is afforded
reasonable advance notice thereof and an opportunity to comment on the form and
substance thereof.

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     7.10 Survival. Sections 2.2(b) and 3 will survive the termination of this
Agreement and/or the expiration of the Holding Period.

     7.11 Expenses. Promptly after the receipt of reasonable substantiating
documentation, the Company will reimburse the Shareholder for up to $50,000 of
its reasonable costs and expenses incurred in connection with its negotiation of
this Agreement.

[Signatures on following page]

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     IN WITNESS WHEREOF, each party has caused its respective duly authorized
representative to execute this Shareholder Agreement as of the date first above
written.

              GENCORP INC.
 
       

  By:            /s/ Terry L. Hall    

       

      Terry L. Hall, Chairman of the Board,

      Chief Executive Officer and President
 
            STEEL PARTNERS II, L.P.
 
            By: Steel Partners, L.L.C., its General Partner
 
       

  By:            /s/ Warren G. Lichtenstein    

       

      Warren G. Lichtenstein, Managing Member

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