The Military Order of the Loyal Legion of the United States (MOLLUS), or, simply, the Loyal Legion, is a United States military order organized on April 15, 1865, by three veteran officers of the Union Army. The original membership was composed of commissioned officers of the Regular or Volunteer Army, U.S. Navy, or U.S. Marine Corps who served during the American Civil War, or who had served and thereafter been commissioned and who thereby "had aided in maintaining the honor, integrity, and supremacy of the national movement" during the Civil War.
 The Loyal Legion was formed in response to rumors from Washington of a conspiracy to incapacitate the United States government by the assassination of its leaders in the immediate aftermath of the assassination of President Abraham Lincoln. The founding members stated their purpose as cherishing the memories and associations of the war waged in defense of the unity and indivisibility of the Republic; the strengthening of the ties of fraternal fellowship and sympathy formed by companionship in arms; the relief of the widows and children of dead companions of the order; and the advancement of the general welfare of the soldiers and sailors of the United States. The veterans' organization became a hereditary society after the original officers died off. The modern organization is composed of men who are direct descendants, nephews, or first cousins of these officers (hereditary members), and also other men who share the ideals of the Order (Associate members), who collectively are considered "Companions". A female auxiliary, Dames of the Loyal Legion of the United States (DOLLUS), was formed in 1899 and accepted as an affiliate in 1915.
 Following the assassination of President Abraham Lincoln on April 14, 1865, rumors spread that the act had been part of a broader conspiracy to overthrow the legally constituted government of the United States by assassinating its chief men. Many people at first gave credence to these rumors, including three of the officers assigned to the honor guard for Lincoln's body as it was transported to Springfield, Illinois, for burial; these three men, Brevet Lt. Col. Samuel Brown Wylie Mitchell, Lt. Col. Thomas Ellwood Zell, and Captain Peter Dirck Keyser, are considered the founders of the Order. To demonstrate their loyalty, they decided to form a "Legion" modeled on the Revolutionary War Society of the Cincinnati. The Loyal Legion was organized mainly during the same meetings that planned Lincoln's funeral and during a mass meeting of Philadelphia war veterans on April 20, culminating in a meeting on May 31, 1865, in Independence Hall in Philadelphia, at which the name was chosen.
 The Order initially was composed of three classes of members:
 The Loyal Legion grew rapidly in the late 19th century and had Companions in every Northern state and many of the states that had once formed the Confederacy. The Commandery in Chief was established on October 21, 1885, with authority over the 14 state commanderies. Previously, the Pennsylvania Commandery functioned as the "first among equals" of the commanderies as it was both the oldest and largest.
 At its height about 1900, the Order had more than 8,000 Civil War veterans as active members, including nearly all notable general and flag officers and several presidents: Ulysses S. Grant, William T. Sherman, Philip H. Sheridan, George H. Thomas, George B. McClellan, Rutherford B. Hayes, Chester A. Arthur, Benjamin Harrison, and William McKinley. The Order's fame was significant enough to inspire John Philip Sousa to compose the "Loyal Legion March" in its honor in 1890.
 The Loyal Legion is one the oldest hereditary military societies in the United States. Predecessors to it include the Society of the Cincinnati, instituted in 1783, and the Aztec Club of 1847, both similarly founded by and for commissioned officers of the United States military.
 Today, the Order serves as a hereditary society (male relatives of eligible officers) rather than as a functioning military order (though many Companions are either military veterans or on active military duty). Among other activities, Companions organize and participate in commemorative events, provide awards to deserving ROTC cadets, and assist with preservation efforts. Of particular note is that each year, the Loyal Legion commemorates President Lincoln's birthday with a wreath-laying ceremony at the Lincoln Memorial in Washington, D.C. In 2009, the MOLLUS helped coordinate an extended tribute with the help of the Abraham Lincoln Bicentennial Commission to celebrate the two-hundredth anniversary of Lincoln's birthday.
 There are now three basic categories of membership:  Hereditary, Associate (non-hereditary), and Honorary. Just as many Original Companions of the Order were also members of the Grand Army of the Republic (the "GAR"), many current Companions of the Order are also members of the Sons of Union Veterans of the Civil War (SUVCW), the legal heir to the GAR.
 Organizationally, the Loyal Legion is composed of a National Commandery-in-Chief and individual state Commanderies. There are currently 20 state Commanderies. Current national officers for the 2023–2025 term include Commander-in-Chief Michael Timothy Bates, Esq, of New Jersey; Senior Vice-Commander-in-Chief Paul Davis of Michigan; Junior Vice-Commander-in-Chief William F. Forbes of Pennsylvania; Treasurer-in-Chief Lee Alan Tryon, CPA, of Connecticut; Recorder-in-Chief Gary L. Grove, PhD. of Pennsylvania; Registrar-in-Chief Jefferson Davis Lilly II, MPA, of Indiana; Judge Advocate-in-Chief Matthew D. Dupee of Pennsylvania; Surgeon-in-Chief Peter B. Kane of Pennsylvania; and Chaplain-in-Chief Jeffry C. Burden, Esq. of Virginia.
 Note – the ranks indicated are the highest the individual held in the United States armed forces or in state militia service and not necessarily the highest rank held during the Civil War.
 Note – Presidents Andrew Johnson and James Garfield were both generals in the U.S. Army during the Civil War and were thus eligible to be veteran companions of MOLLUS but did not join the Order.
 In addition to the above, President Andrew Johnson, vice president before President Lincoln's death and the founding of MOLLUS, was eligible to become a First Class Companion of MOLLUS but did not join the Order. President Chester A. Arthur, who was vice president prior to the death of President Garfield, was elected in 1882 as a 3rd Class Companion while serving as president.
 A limited number of individuals may be elected as Honorary Companions of MOLLUS. They are usually individuals with distinguished careers in public service or the military.
 Note – The rank indicated is the highest held in the Regular Army, the Volunteers, or in retirement.
 From 1865 to 1890, a limited number of civilians who contributed outstanding service to the United States during the Civil War were elected into the Order as 3rd Class Companions.
 Initially, the MOLLUS had Companions of the Second Class, the eldest sons of Companions of the First Class (i.e., veterans of the Civil War who also held a commission at some point). A Second Class Companion became a First Class Companion upon his father's death, and brothers of fallen officers were allowed to join as hereditary companions if there was no surviving issue. These practices were discontinued in 1905 when the MOLLUS Constitution was changed to allow any direct male descendant of a U.S. Army officer to become a MOLLUS Companion. The nomenclature of First Class and Second Class Companions was discarded, leaving only the qualifiers of "Original" and "Hereditary" Companions. Later, the eligibility rules were changed to allow nephews of U.S. officers to become hereditary Companions of the MOLLUS; and as of October 2021, a first-cousin relationship to an officer (i.e., the officer was the child of the aunt or uncle of the applicant) qualifies the applicant for hereditary membership.
 MOLLUS allows state commanderies, at their discretion, to elect up to one-third of their membership as Associate Companions.
 Several noteworthy Union officers, although eligible, did not become MOLLUS companions. They included the following:
 Brigadier General and President Andrew Johnson, Major General and President James Garfield, Major General and United States Senator Francis Preston Blair Jr., Brevet Brigadier General Kit Carson, Major General John A. Dix, Acting Ensign Pierre d'Orleans, Duke of Penthièvre, Rear Admiral Samuel Dupont, Major General John G. Foster, Major General John C. Fremont, Captain Charles Vernon Gridley USN, Brevet Major General William S. Harney, Rear Admiral Alfred Thayer Mahan, Major General George Meade, Major General and Governor Edwin D. Morgan, Major General Edward Ord, Major General Daniel Sickles, Brevet Major General Emory Upton, Brevet Brigadier General Thomas J. Rodman, Brevet Brigadier General Sylvanus Thayer, Captain Augustin Thompson, Brevet Major General Zealous Bates Tower, Acting Assistant Third Engineer George Westinghouse, Rear Admiral John Ancrum Winslow, Major General John E. Wool.
 Major General George Meade was posthumously inducted as a MOLLUS companion in 2015.
 William Waldorf Astor, 1st Viscount Astor was, and his male descendants are, eligible for hereditary membership in MOLLUS by right of his father's service in the U.S. Army. All other male descendants of Rear Admiral Winfield Scott Schley
and William Backhouse Astor Sr. are eligible for membership in MOLLUS by collateral descent.
 All male descendants of 19th-century railroad tycoon Cornelius Vanderbilt are eligible to join MOLLUS as collateral descendants of Vanderbilt's youngest son, Captain George Washington Vanderbilt, who graduated West Point in 1860 and died on January 1, 1864, in Nice, France without issue. These descendants include the current Duke of Marlborough and CNN reporter Anderson Cooper. Anderson Cooper is also eligible for hereditary membership in MOLLUS because of his descent from Major General Hugh Judson Kilpatrick.
 Major General David D. Porter, USMC, a recipient of the Medal of Honor, was eligible for membership in MOLLUS by right of his descent from his grandfather, Admiral David Dixon Porter.
 Secretary of State John Foster Dulles and his brother, CIA Director Allen Dulles, were eligible for membership in MOLLUS by right of their descent from their maternal grandfather Colonel John W. Foster, who served as Secretary of State in the administration of President Benjamin Harrison.
 Vice-president of the United States Richard (Dick) Cheney, by right of descent from Captain Samuel Fletcher Cheney of the 21st Ohio Volunteer Infantry.
 John Bouvier Kennedy Schlossberg, grandson of President John F. Kennedy, by right of descent from Captain John V. Bouvier of the 80th New York Volunteer Infantry (20th New York State Militia). Captain Bouvier was the great-grandfather of First Lady Jacqueline Bouvier Kennedy.
 Several Europeans of royal descent at eligible for membership in MOLLUS by right of their descent from Captain Philippe d'Orleans, the grandson of King Louis Philippe I of France.
 King Felipe VI of Spain and his father, former King of Spain Juan Carlos, are eligible for hereditary companionship in MOLLUS, as are their male descendants. The same is true for the family of the Orleanist pretenders to the throne of France.
 King Manuel II of Portugal (1889–1932) was eligible to become a hereditary companion of MOLLUS as his mother was a daughter of Philippe d'Orleans. He had no offspring.
 Prince Pedro Carlos of Orléans-Braganza (b. 1945) is a claimant to the Brazilian throne and a descendant of Philippe d'Orleans. His nephew is Peter, Hereditary Prince of Yugoslavia (b. 1980).
 Prince Amedeo, Duke of Aosta (1943-2021), head of the House of Savoy and claimant to the throne of Italy, was eligible for hereditary MOLLUS membership but was elected as an honorary member instead.
 Several other individuals of royal descent can join MOLLUS by right of their descent from Prince Robert, Duke of Chartres – the brother of Prince Philippe, who also served with the Union Army. These descendants included Prince Michael of Greece and Denmark (b. 1938) and previously included Henri, Count of Paris (1908–1999) (longtime pretender to the French throne), Count Aage of Rosenborg (1887–1940) (who served as an officer in the French Foreign Legion), and Prince Axel of Denmark (1888–1964).
 Prince Pierre, Duke of Penthièvre was a cousin of the Count of Paris and served in the Union Navy as an ensign on the frigate USS John Adams.
 Jean d'Orleans (b. 1965) is the current Count of Paris and Orleanist pretender to the French throne.