Romanian-born American screenwriter who worked with director Billy Wilder (Wilder, Billy) to produce such motion pictures as Love in the Afternoon (1957), Some Like It Hot (1959), and The Apartment (1960), for which he won an Academy Award for best screenplay.

Before graduating from Columbia University (1941), Diamond wrote for The Columbia Spectator and adopted the initials I.A.L. as his legal name. He wrote scripts for such films as Murder in the Blue Room (1944) and Always Together (1947) before embarking on a 30-year collaboration with Wilder. The two combined witty dialogue with sexual situations and explored male-female relationships, combining cynicism with sentiment. Some of their other films include Irma La Douce (1963), The Fortune Cookie (1966), The Private Life of Sherlock Holmes (1970), Avanti! (1972), The Front Page (1974), Fedora (1978), and Buddy Buddy (1981).