Louis Burt Mayer (; born Lazar Meir; July 12, 1882 or 1884 or 1885 – October 29, 1957) was a Canadian-American film producer and co-founder of Metro-Goldwyn-Mayer studios (MGM) in 1924. Under Mayer's management, MGM became the film industry's most prestigious movie studio, accumulating the largest concentration of leading writers, directors, and stars in Hollywood.

Mayer was born in the Russian Empire and grew up poor in Saint John, New Brunswick. He quit school at 12 to support his family and later moved to Boston and purchased a small vaudeville theatre in Haverhill, Massachusetts, called the "Garlic Box" because it catered to poorer Italian immigrants. He renovated and expanded several other theatres in the Boston area catering to audiences of higher social classes. After expanding and moving to Los Angeles, he teamed with film producer Irving Thalberg and they developed hundreds of high-quality story-based films, known for their wholesome and lush entertainment. Mayer handled the business of running the studio, such as setting budgets and approving new productions, while Thalberg, still in his twenties, supervised all MGM productions.

During his long reign at MGM, Mayer acquired many enemies as well as admirers. Some stars did not appreciate his attempts to control their private lives, while others saw him as a concerned father figure. He believed in wholesome entertainment and went to great lengths to discover new actors and develop them into major stars. He also forced compliance from female stars by threatening their livelihoods, and sexually abused Judy Garland, whom he forced to go on diets, take drugs, and work punishing schedules.

Mayer was forced to resign as MGM's vice president in 1951, when the studio's parent company, Loew's, Inc., wanted to improve declining profits. A staunch conservative, Mayer at one time was the chairman of the California Republican Party. In 1927 he was one of the founders of AMPAS, famous for its annual Academy Awards.