Jack Leonard "J.L." Warner , born Jacob Warner in London, Ontario, Canada, was the president and driving force behind the successful development of Warner Brothers Studios in Hollywood, Los Angeles, California. Warner's 45-year career was lengthier than that of any other traditional Hollywood studio mogul.

As co-head of production at Warner Bros. Studios, he worked with his brother, Sam Warner, to procure the technology for the film industry's first talking picture. After Sam's death, Jack clashed with his surviving older brothers, Harry and Albert Warner. He assumed exclusive control of the film production company in the 1950s, when he secretly purchased his brothers' shares in the business after convincing them to participate in a joint sale of stocks.