Lloyd Lionel Gaines (born 1911 – disappeared March 19, 1939) was the plaintiff in Gaines v. Canada (1938), one of the most important early court cases in the 20th-century U.S. civil rights movement. After being denied admission to the University of Missouri School of Law because he was African American, and refusing the university's offer to pay for him to attend a neighboring state's law school that had no racial restriction, Gaines filed suit. The U.S. Supreme Court ultimately ruled in his favor, holding that the separate but equal doctrine required that Missouri either admit him or set up a separate law school for black students.

The Missouri General Assembly chose the latter option. It authorized conversion of a former cosmetology school in St. Louis to establish the Lincoln University School of Law, to which other, mostly black, students were admitted. The National Association for the Advancement of Colored People (NAACP), which had supported Gaines's suit, planned to file another one challenging the adequacy of the new law school. While waiting for classes to begin, Gaines traveled between St. Louis, Kansas City and Chicago looking for work. He worked odd jobs and gave speeches before local NAACP chapters. One night in Chicago he left the fraternity house where he was staying and never returned. He was never seen again by anyone who knew or recognized him.

Gaines's disappearance was not noted immediately, since he frequently traveled independently and alone, without telling anyone his plans. Only in late 1939, when the NAACP's lawyers were unable to locate him to take depositions for a rehearing in state court, did a serious search begin. It failed, and the suit was dismissed. While most of his family believed at the time that he had been killed in retaliation for his legal victory, there has been speculation that Gaines had tired of his role in the movement and gone elsewhere, either New York or Mexico City, to start a new life. In 2007 the Federal Bureau of Investigation (FBI) agreed to look into the case, among many other missing persons cold cases related to the civil rights era.

His unknown fate notwithstanding, Gaines has been honored by the University of Missouri School of Law and the state. The Black Culture Center at the University of Missouri and a scholarship at its law school are named for him and another black student initially denied admission. In 2006 Gaines was posthumously granted an honorary law degree. The state bar granted him a posthumous law license. A portrait of Gaines hangs in the University of Missouri law school building.

Born in 1911 in Water Valley, Mississippi, Gaines moved with his mother, Callie Gaines, and siblings to St. Louis, Missouri, in 1926 after the death of their father, Henry Gaines. Part of the Great Migration from rural communities in the South to industrial cities in the North, his family settled in the city's Central West End neighborhood. Gaines did well academically, and was a valedictorian at Vashon High School, one of the two historically all-black high schools in the area.

Gaines was placed in the fifth grade at fifteen years old because of his education in Mississippi. He caught up quickly, completing four years of grammar school in only two years and four years of high school in only three. While Gaines supported his family with an after-school job, he graduated first in his class.

After winning a $250 ($5,000 in current dollars) scholarship in an essay contest, Gaines went to college. He attended Stowe Teachers College in St. Louis for one year before transferring. He graduated with honors and a bachelor's in history from Lincoln University, a historically black college in Jefferson City, Missouri. It was the state's segregated undergraduate institution for African Americans.

To cover the gap between his scholarship and the college's tuition, he sold magazines on the street. Gaines was elected as president of the senior class and a brother in the Alpha Phi Alpha fraternity.