Born in New York, raised in Philadelphia, Mulligan was the foremost baritone sax player of his generation, as well as an acclaimed composer and arranger, and one of the founders of the post-WWII "West Coast" school of jazz. In addition to his three marriages, Mulligan was the long-term lover of actress Judy Holliday, an affair which began in 1958 and ended with her death. When she became terminally ill in the 1960s, he put his own career on hold to nurse her until the end.