According to Wikipedia:
Seven Arts Productions was founded in 1957 by Ray Stark and Eliot Hyman. The company was a frequent producer of movies for other studios, including Lolita for Metro-Goldwyn-Mayer, The Misfits for United Artists, and Is Paris Burning for Paramount Pictures. Over time they expanded their involvement in movies from just being producers to becoming equity investors with the studios, partnering with legendary horror film company Hammer Film Productions on many projects, and producing Seven Days in May and Promise Her Anything for release by Paramount; on these productions, they retained ancillary rights that they had surrendered on earlier films.
In 1967 they acquired Jack Warner's controlling interest in Warner Bros. for $95 million and merged with it, becoming Warner Bros.-Seven Arts.