Remembered for his recurring role as George on the early 1960s CBS sitcom Angel, Keefer is also notable for his numerous guest spots on the western series Gunsmoke.
He made his cinematic debut in the 1951 movie Death of a Salesman and also appeared early in his career in episodes of the television series Appointment with Adventure and Richard Diamond, Private Detective.
He was one of the original members of the famous Actors Studio.
A native of Highspire, Pennsylvania, he later settled in Los Angeles, California. His four-decade marriage to screen actress Catherine McLeod resulted in sons named Thomas, John, and Donald.
He appeared with Rod Cameron in an episode of the television series State Trooper.