Born in Harrah, Okla., Robertson enrolled in Oklahoma Military College at age 17 and made his living early on as a professional prize fighter. In World War II, he fought for the U.S. Army in North Africa and Europe and was awarded the Bronze and Silver Stars and the Purple Heart for injuries he suffered during his service, the AP reports.
He was recruited into Hollywood by movie scouts who saw a picture he had taken for his mother in a photo shop window, according to the AP. Robertson's film credits include playing Jesse James in 1949's Fighting Man of the Plans. He also starred alongside Joan Crawford in Flamingo Road.
Once he transitioned to television in the 1950s, Robertson landed roles in such series as Tales of Wells Fargo, Iron Horse and Death Valley Days. Later, he also starred on Dallas and Dynasty. His final role before retirement was playing Zeke in Harts of the West in the early 1990s. After retiring, he lived on his ranch in Yukon, Okla., and moved to the San Diego area last year.
Robertson was later inducted into the Hall of Great Western Performers and the Cowboy Hall of Fame in Oklahoma City.
He is survived by a wife, Susan Robbins, and two children.