Played mystery novelist Dashiell Hammett twice; first as the lead in Hammett (1982), then as a supporting role in Citizen Cohn (1992).
Has a collection of James Dean memorabilia and more than 200 hats.
In Apocalypse Now (1979), his character ("Chef") is yelling for the Playboy Playmates from the crowd, and one of them is played by Colleen Camp, who, in four years, would be his contented hippie wife in Valley Girl (1983).
Although he had a relatively small role in The Conversation (1974), it is an extremely important one: He and Cindy Williams are the two people having that titular conversation (recorded by Gene Hackman: so Forrest's and Williams's voices are heard throughout the film).
Is part of Francis Ford Coppola's Zoetrope family, having appeared in The Conversation (1974), Apocalypse Now (1979), and One from the Heart (1981), which were directed by Coppola, and The Stone Boy (1984), which Coppola produced.
In 1986-87, he spent a lot of time playing law enforcement agents on television: As real life Detective Bob Keppell in the Ted Bundy two-part television movie, The Deliberate Stranger (1986), and as the fictional Captain Richard Jenko on 21 Jump Street (1987).
In Apocalypse Now (1979), his character ("Chef") shouts the line, "Never Get Out Of The Boat!", which is later recited by Captain Willard (played by Martin Sheen).
Appeared for the first time at the popular Hollywood Show (Autograph Convention in Los Angeles) in 2018.
In 1976, in the quirky Western The Missouri Breaks (1976), he plays part of a group of men being hunted by Marlon Brando. That same year, Apocalypse Now (1979), started filming (to be released in 1979), where he plays part of a group of men who are hunting Brando.
Acted with Jack Nicholson in Arthur Penn's The Missouri Breaks (1976), and then acted with and directed Nicholson in the Chinatown remake, The Two Jakes (1990).
Acted in two movies with Robert Duvall, Apocalypse Now (1979), and Falling Down (1993); however their characters do not interact or share scenes. Also acted with Robert Duvall in the miniseries Lonesome Dove (1989).
In both The Don Is Dead (1973) and The Dion Brothers (aka The Gravy Train (1974)) Forrest played one of a pair of outlaw brothers, with Al Lettieri and Stacy Keach, respectively.
Appeared alongside Harry Dean Stanton in two movies that weren't initially well-received but have since acquired a cult following: The Missouri Breaks (1976), and One from the Heart (1981). They played good buddies in both.