William Martin Gulager, known as Clu Gulager, was born in Holdenville, Hughes County, Oklahoma, with the nickname given to him by his father for the clu-clu birds nesting at the Gulager home at the time of his birth. Growing up on his uncle's ranch as a cowhand, Gulager later joined the United States Marine Corps from 1946-1948 and developed an interest in acting during his time in the army.
After leaving the Marines, Gulager used the GI Bill of Rights to study acting, during which time he met his future wife, actress Miriam Byrd-Nethery. The couple married in 1952 and had two children, John and Tom, and were married for over 50 years until Miriam's passing in 2003 due to cancer.
Gulager's early career consisted of bit parts on popular western shows, typically playing the heavy. He later gained recognition for his role as "Mad Dog Coll" on The Untouchables, which led to him being cast as "Billy the Kid" on The Tall Man from 1960-1962.
Gulager's next significant role was as Deputy Emmett Ryker on The Virginian from 1964-1968, during which time he also appeared in the 1964 TV film The Killers alongside Lee Marvin. Gulager's work in television and film continued throughout the 1970s and 1980s, with notable roles in The Last Picture Show, McQ, and A Force of One.
In the 1980s, Gulager began to focus on horror films, following in the footsteps of other TV actors who had transitioned to B-movies and late-night horror films. He landed a lead role in Dan O'Bannon's cult classic The Return of the Living Dead in 1985 and also appeared in A Nightmare on Elm Street Part 2: Freddy's Revenge.
Throughout the 1980s and 1990s, Gulager continued to act in television and occasional horror films. In his 80s, he began acting in his son's horror films, including the Feasts movies and Piranha DD, and remained a horror fan favorite, attending conventions until almost 90 years old.