The Military Order of the Loyal Legion of the United States, (MOLLUS), or simply as the Loyal Legion is a United States patriotic order, organized April 15, 1865, by officers of the Army, Navy, or Marine Corps of the United States who "had aided in maintaining the honor, integrity, and supremacy of the national movement" during the American Civil War. It was formed by loyal union military officers in response to rumors from Washington of a conspiracy to destroy the Federal government by assassination of its leaders, in the immediate aftermath of the assassination of President Abraham Lincoln. They stated their purpose as the cherishing of 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. As the original officers died off, the veterans organization became an all-male hereditary society. The modern organization is composed of male descendants of these officers (hereditary members), and others 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 wider 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 largely during the same meetings that planned Lincoln's funeral (as well as 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.