Gulager served in the United States Marine Corps at Camp Pendleton. After attending Northeastern State University in Tahlequah, Oklahoma, Gulager transferred to the 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. On June 19, 1952, he married fellow actor Miriam Byrd-Nethery. The couple had two sons, John and Tom, and remained married until her death in 2003. Career In 1958 he 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. Gulager stated, "Lew Wasserman saw me on a Playhouse 90 episode where I played an Elvis Presley-type character. I became the first contract player at Universal". In the spring of 1959, he signed with MCA-TV, where he 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 López de Santa Anna in Mexico threaten to blow up Holden's vessel, the Enterprise. From 1960 to 1962, 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 (1943) and The Left Handed Gun