He is best known for starring alongside John Wayne in the films Sands of Iwo Jima, Fort Apache, and She Wore a Yellow Ribbon.
In his later career he was the star of B movies, such as Tarantula!, The Mole People, The Brain from Planet Arous, Revenge of the Creature, Flesh and the Spur and Hand of Death.
Agar's career suffered in the wake of his divorce, but he developed a niche playing leading men in low-budget science fiction, Western, and horror movies in the 1950s and 1960s.
[13] Agar was reunited with Temple for his second film, a suffragette drama Adventure in Baltimore (1949), also for RKO, which was a huge flop.
[13] Even more popular was the World War II film Sands of Iwo Jima (1949) where Agar supported John Wayne.
Made by Republic Pictures, it was a sizeable hit, earning Wayne an Oscar nomination and getting Agar some good reviews.
He made a low budget Arabian Knights film for Sam Katzman with Lucille Ball, The Magic Carpet (1951).
[15] Agar was third billed in Woman of the North Country (1952), a Western for Republic, and also starred in Man of Conflict (1953), an independent drama with Edward Arnold.
Agar had support roles in Bait (1954), a Hugo Haas drama with Cleo Moore; The Rocket Man (1954), a Charles Coburn comedy co-written by Lenny Bruce; and Shield for Murder (1954), a film noir starring and co-directed by Edmond O'Brien.
He was borrowed by Lippert Pictures for The Lonesome Trail (1955), then, at Universal, made a second film for Haas with Cleo Moore, Hold Back Tomorrow (1955).
[16] His final film with the studio was supporting Universal's Western star Audie Murphy in a comedy Joe Butterfly (1957).
He starred in The Daughter of Dr. Jekyll (1957) for Edgar G. Ulmer at Allied Artists, then made The Brain from Planet Arous (1957) for Howco International.
He joined he ensemble casts in several low budget films for producer A.C. Lyles that were released by Paramount Pictures; The Young and The Brave (1963) with Rory Calhoun, Law of the Lawless (1963) starring Dale Robertson and William Bendix, Stage to Thunder Rock (1965) with Barry Sullivan and Marilyn Maxwell, Young Fury (1965) with Rory Calhoun and Lon Chaney Jr., Johnny Reno (1966) with Dana Andrews and Jane Russell, and Waco (1966) with Howard Keel, Jane Russell and Brian Donlevy.
He made some films for Larry Buchanan at AIP that were originally meant as made-for-television-movies, Curse of the Swamp Creature (1966), Zontar, the Thing from Venus (1966) and Hell Raiders (1968).
He had small parts in some studio films like The St. Valentine's Day Massacre (1967) with Jason Robards Jr. and Ralph Meeker, and three more pictures in a row with John Wayne: The Undefeated (1969), Chisum (1970), and Big Jake (1971).
[29] Agar died on April 7, 2002, in Burbank, California from severe complications from emphysema, after being confined for months to an iron lung.
[31] The television series Mystery Science Theater 3000 has featured several of Agar's films, including The Mole People, Women of the Prehistoric Planet and Revenge of the Creature.