Clu Gulager was born William Martin Gulager in Holdenville, Hughes County, Oklahoma. His 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 Clu was born. He grew up on his uncle's ranch as a cowhand and when he was old enough he joined the United States Marine Corps for a stint from 1946-1948. He got the acting bug being in army plays so when he left he used the GI Bill of Rights to study acting. During this time he met his wife, actress Miriam Byrd-Nethery. They wed in 1952 and had two children: John (born 1957) and Tom (born 1965) The couple was married for more than 50 years until her death in 2003 from cancer.
Gulager's career started off as bit parts on popular western shows usually playing the heavy. Shows like Wanted Dead or Alive, Have Gun Will Travel, Laramie, Riverboat. He scored big with The Untouchables as "Mad Dog Coll", which led to him being offered the role