Louis Burt Mayer (born Lazar Meir July 4, 1884 – October 29, 1957) was an early film producer, most famous for his stewardship and co-founding of the Hollywood film studio Metro-Goldwyn-Mayer.

He is generally cited as the creator of the "star system" within Metro-Goldwyn-Mayer (MGM) in its golden years. Known always as Louis B. Mayer and often simply as "L.B.", he believed in "wholesome entertainment" and went to great lengths so that MGM had "more stars than there are in the heavens".

Born to a Jewish family in Minsk, today the capital of Belarus, then in the Russian Empire, capital of the Minsk Province (Minskaja Guberniya). His actual birthdate is unknown; a patriotic Mayer chose July 4 when he became an American citizen, to honor his adopted country. Mayer emigrated with his family to Saint John, New Brunswick, Canada when he was still very young, and Mayer attended school there. His father started a scrap metal business, J. Mayer & Son. His parents, Sarah and Jacob Mayer, had five children: Yetta, Ida, Louis, Jerry and Rudolph. In 1904, the 19-year-old Mayer left St. John for Boston, where continued for a time in the scrap metal business, married, and took a variety of odd jobs to support his family when his junk business lagged.