John O’Brien, a composer and music supervisor for film and TV who provided material for “Iron Man” and its sequel, “Pineapple Express,” “Four Christmases” and “Couples Retreat,” was found dead on Saturday in a Chicago hotel room by film producer and former child actor Peter Billingsley. He was 45.

Billingsley discovered O’Brien in his room at the Millennium Knickerbocker Hotel in downtown Chicago. An autopsy was inconclusive, but toxicological studies are pending, and suspected narcotics and sleeping pills were found in the room, according to the Chicago Tribune.

O’Brien worked with Billingsley and actor-director Jon Favreau on a number of films beginning with “Made” in 2001, 2006’s “The Break-Up,” 2008’s “Four Christmases”; both “Iron Man” pics; and “Couples Retreat.”

O’Brien earned his first screen credits on 1997 film “Nightwatch” and 1999’s “Anywhere but Here.”

He also worked in TV, acting as music supervisor on ABC’s brief David Arquette series “In Case of Emergency” in 2007 and composing the theme music for last season’s “Detroit 1-8-7.”

O’Brien most recently worked as music supervisor on the Will Arnett-Christina Applegate sitcom “Up All Night,” which NBC will premiere Sept. 14.