The Iran hostage crisis was a diplomatic standoff between Iran and the United States.
 Fifty-two American diplomats and citizens were held hostage for 444 days from November 4, 1979, to January 20, 1981 after a group of Iranian students belonging to the Muslim Student Followers of the Imam's Line, who supported the Iranian Revolution, took over the U.S. Embassy in Tehran.
 It stands as the longest hostage crisis in recorded history.
Al-Maziri (1061 – 1141 CE) (453 AH – 536 AH ), also known as Imam al-Maziri and Imam al-Mazari was an important Tunisian jurist in the Maliki school of Sunni Islamic Law.
 He was one of the most important figures in the school and his opinions are well known and respected to this day.
 Al-Maziri was one of four jurists whose positions were held as authoritative by Khalil ibn Ishaq in his Mukhtassar, which is the most important of the later texts in the relied upon positions of the school.
 It is for this reason that he is referred to simply as "al-Imam" (the Imam) within the Maliki school.
The Muslim Student Followers of the Imam's Line (Persian: دانشجویان مسلمان پیرو خط امام‎ ‎ "Dânešjuyân Mosalmân Piru Xatt Emâm"), also called the Muslim Students of the Imam Khomeini Line, was an Iranian student group that occupied the U.S. embassy in Tehran on 4 November 1979.
 The students were supporters of the Islamic Revolution who occupied the embassy to show their support for Ayatollah Khomeini and their outrage that the ex-Shah of Iran was admitted to the United States for cancer treatment, instead of being returned to Iran for trial and execution.
 The occupation triggered the Iran hostage crisis where 52 American diplomats and citizens were held hostage for 444 days.
Rukn al-Dīn Khurshāh (Arabic: ركن الدين خورشاه‎ ‎ ) or Rukn al-Dīn Khwarshāh (Persian: رکن‌الدین خورشاه‎ ‎ ) (?
-1256) was the son of ‘Alā’ ad-Dīn Muḥammad III and the 27th Nizari Shiʿi Imam.
 He was also the fifth and final Imam who ruled at Alamut.
 The Imam was the eldest son of Imam ʿAla al-Din Muhammad and succeeded his murdered father to the Imamate in 1255.
 Imam Rukn al-Din engaged in a long series of negotiations with the invading Mongols, and under whose leadership Alamut Castle was surrendered to the Mongol Empire.
Mohammad Hashemi (Persian: محمد هاشمی‎ ‎ ) is an Iranian businessman and former intelligence officer.
 He was one of "the core group of leaders" of the Muslim Student Followers of the Imam's Line involved in the Iran Hostage Crisis, the first deputy of the Ministry of Intelligence and Security for some years.
 From 2003 to 2004, when the venture went bankrupt, he was a developer of a proposed vacation resort on the Caspian Sea called Cham Paradise.
 He is the husband of Masoumeh Ebtekar, another well-known Iranian and former spokesperson for the hostage takers.
Ali ibn Husayn (Arabic: علي بن الحسين‎ ‎ ) known as Zayn al-Abidin (the adornment of the worshippers) and Imam al-Sajjad (The Prostrating Imam), was the fourth Shia Imam, after his father Husayn, his uncle Hasan, and his grandfather Ali.
 Ali ibn Husayn survived the Battle of Karbala and was taken to the caliph in Damascus.
 Eventually, he was allowed to return to Medina, where he led a secluded life with a few intimate companions.
 Imam Sajjad's life and statements were entirely devoted to asceticism and religious teachings, mostly in the form of invocations and supplications.
 His famous supplications are known as Al-Sahifa al-Sajjadiyya.
Qasīdat al-Burda (Arabic: قصيدة البردة‎ ‎ , "Poem of the Mantle"), or al-Burda for short, is an ode of praise for the Islamic prophet Muhammad composed by the eminent Sufi mystic Imam al-Busiri of Egypt.
 The poem whose actual title is "al-Kawākib ad-Durrīya fī Madḥ Khayr al-Barīya" (الكواكب الدرية في مدح خير البرية , "The Celestial Lights in Praise of the Best of Creation"), is famous mainly in the Sunni Muslim world.
 It is entirely in praise of Muhammad, who is said to have cured the poet of paralysis by appearing to him in a dream and wrapping him in a mantle or cloak.
 Bānat Suʿād, a poem composed by Ka'b bin Zuhayr was originally called as Al-Burdah.
 He recited this poem in front of Muhammad after embracing Islam.
 Muhammad was so moved that he removed his mantle and wrapped it over him.
 The original Burdah is not as famous as the one composed by Imam al-Busiri even though Muhammad had physically wrapped his mantle over Ka'b not in a dream like in case of Imam al-Busiri.
Richard Henry Morefield (September 9, 1929 – October 11, 2010) served in the United States Foreign Service and was one of the 66 staff members at the American embassy in Teheran who were taken captive by a militant Islamist student group called the Muslim Student Followers of the Imam's Line on November 4, 1979, as part of what became known as the Iran hostage crisis.
 He was one of 52 Americans who were held as a hostage for 444 days, until negotiations for the remaining captives being held hostage were concluded with the signing of the Algiers Accords on January 19, 1981, with their release coming the following day.
Alan Henning (15 August 1967 – c. 3 October 2014) was an English taxicab driver-turned-volunteer humanitarian aid worker.
 He was the fourth Western hostage killed by Islamic State of Iraq and the Levant (ISIL) whose killing was publicised in a beheading video.
Shakeel Begg has been Imam at the influential Lewisham Islamic centre in London UK since 1998, and has played a prominent role in the UK Muslim community, and has been invited to speak at many Mosques and Islamic events, and been a spokesman for the Muslim community in many events and press releases: including high-profile attempts to secure the release by ISIS of British hostage Alan Henning.

Question: What imam worked to release the hostage whose beheading was the fourth to be videotaped?
Answer: Shakeel Begg