His Cherokee nickname was given to him by his father for the clu-clu birds (known in English as martins, like his middle name) that were nesting at the Gulager home at the time of his birth. From 1946 to 1948, Gulager served in the United States Marine Corps. After attending Northeastern State University in Tahlequah, Oklahoma, Gulager transferred to Baptist-affiliated Baylor University in Waco, Texas, where he graduated. He won a one-year scholarship to study abroad in Paris, where he worked under Jean Louis Barrault, a French actor and director. In 1952, he returned to Baylor. In 1960, he married fellow actor Miriam Byrd Nethery, an Arkansan. The couple had two sons, including film director John Gulager, and remained married until her death in 2003.

In 1958, Gulager appeared as Roy Carter in the episode “The Return of Roy Carter” (written by Gene Roddenberry, creator of Star Trek) in the Western television series Have Gun – Will Travel starring Richard Boone. In the spring of 1959, Gulager appeared as Tommy Pavlock in the episode “The Immigrant” of NBC’s series The Lawless Years, a 1920s crime drama. In the fall of 1959, he appeared in the episode “The Temple of the Swinging Doll” of NBC’s short-lived espionage drama Five Fingers, starring David Hedison.

On June 3, 1959, he guest-starred as the unscrupulous photographer Elliott Garrison in “The Andrew Hale Story” on NBC’s Wagon Train. On October 11, 1959, Gulager appeared as a U.S. Navy sailor in the “Appointment at Eleven” episode of Alfred Hitchcock Presents and again as an escaped convict in “Pen Pal” on November 1, 1960. On The Untouchables, he played the role of real-life vicious mob killer Vincent “Mad Dog” Coll. Gulager was hailed for his utterly chilling performance as the psychopathic Coll. Late in 1959, he was cast as Beau Chandler in the episode “Jessie Quinn” of the NBC Western series Riverboat, starring Darren McGavin and Burt Reynolds. The episode is a tale of intrigue involving the Texas Revolution. Capt. Holden attempts to send weapons to Sam Houston, but forces of Antonio Lopez de Santa Anna in Mexico threaten to blow up Holden’s vessel, the Enterprise.

From 1960-62, Gulager played Billy the Kid in The Tall Man opposite Barry Sullivan as Sheriff Pat Garrett. The episodes portray Billy as a sympathetic character without resorting to the “misunderstood young man” theme used in such films as The Outlaw and The Left Handed Gun. In 1961, Gulager guest-starred in another NBC Western, Whispering Smith, Audie Murphy’s only attempt at series television. Gulager portrayed Deputy Sheriff Emmett Ryker from 1964 to 1968 on The Virginian, the 90-minute Western series in which he starred with James Drury, Doug McClure, Lee J. Cobb, Roberta Shore, Randy Boone, Gary Clarke, and Diane Roter. Gulager appeared more than 60 times in other roles in film and television, including the film Winning and the CBS series Three for the Road. He also appeared several times on NBC’s Bonanza. He starred with Lee Marvin, Ronald Reagan, John Cassavetes, and Angie Dickinson in The Killers, teaming with Marvin as a pair of ruthless hit men.

Gulager appeared notably in The Last Picture Show (1971). In 1977, long after his role on The Virginian, he appeared in Rod Taylor’s unsuccessful NBC Western series, The Oregon Trail, in the episode “The Army Deserter”. Gulager also played the boss of Susan Sarandon in a 1977 film drama, The Other Side of Midnight. In 1981, he co-starred opposite Oscar Award-winner Jane Wyman, along with some newer younger actors Lorenzo Lamas, William R. Moses, and Jamie Rose, in the pilot episode of The Vintage Years (which was retooled as the primetime soap opera: Falcon Crest) for the male lead role of Angela Channing’s long-suffering nephew, Chase Gioberti, when he was not rehired to continue with his role, hence, Robert Foxworth, took over the role, until his firing in 1987. He also appeared in his son John Gulager’s Feast series of films as a shotgun-toting bartender, and had a role in the 2012 film Piranha 3DD. He was also a featured player in director John Landis’ darkly comedic 1985 film noir satire, Into The Night, a film rife with insider Hollywood cameos, as an FBI agent, courier of a cache of clandestine funds, which he grudgingly delivers to secure the safety of the film’s two romantic leads (Michelle Pfeiffer and Jeff Goldblum). In an example of the film’s dry humor, their characters find they are not in a position to object as the agent/courier (Gulager) angrily pilfers as many packets of bills from the treasure trove as he can resentfully stuff into his pockets in plain sight of them, before leaving the bewildered pair in a huff.

He was cast as Burt Wilson in the Dan O’Bannon-directed 1985 cult classic, The Return of the Living Dead. In 2005, Gulager appeared in Feast, followed by the film’s two sequels, Feast II: Sloppy Seconds (2008), and Feast III: The Happy Finish (2009), all of which were directed by his son, John. He also had a minor role in the critically acclaimed independent film Tangerine (2015).