[3] When he was in his early twenties, "Don" moved to New York City, where he attended the American Academy of Dramatic Arts, graduating from that prestigious acting school in 1939.

He also had a small role in Rod Serling’s Twilight Zone prequel “Time Element” in 1958, starring William Benedix, Darryl Hickman and Martin Balsam.

Keefer gave a moving performance as Dan in The Twilight Zone S3 E8 "It's a Good Life" (1961), whose birthday party turns fatal when he opposes six year old Anthony, played by Billy Mumy.

At the time of Catherine's death (following his retirement in acting), the Keefers were living in Sherman Oaks in the San Fernando Valley of Los Angeles County, California.

[8] On Angel, Keefer portrayed the neighbor "George", husband of "Susie", a character played by Doris Singleton, a veteran of the original I Love Lucy series.

Earlier, he had roles in the following three episodes of CBS's The Twilight Zone: as Dan Hollis in "It's a Good Life" (1961), as Spiereto in "Passage on the Lady Anne" (1963), and as Fred Danziger in "From Agnes - With Love" (1964).