According to an article on TV westerns in Time Magazine (March 30, 1959), Robertson stood 6 feet tall, weighed 180 lbs, and had chest-waist-hips measurements of 42-34-34
At the age of 17 he was attending Oklahoma Military College, and boxing in professional prize fights to earn money. Harry Cohn approached him after a fight in Wichita, Kansas and asked him to come out to Hollywood to play the role of Joe Bonaparte in a boxing picture called "Golden Boy." Robertson refused, saying he was in the middle of training 17 polo ponies, and could not leave his family at his age. William Holden eventually was cast in the Golden Boy (1939) role.
Inducted into the Hall of Great Western Performers of the National Cowboy and Western Heritage Museum in 1983.
Robertson entered the U.S. Army during World War II. After stateside training he served as a tank commander in the 777th Tank Battalion in the North African campaign. He was standing in the hatch when his tank was hit by enemy fire. His tank crew were killed, but he was blown out of the hatch and survived with shrapnel wounds to his lower legs, the scars of which he still bears. Fully recovered, he went on to serve with the 322nd Combat Engineer Battalion during the European campaign. He was wounded a second time, this one in the right knee during a mortar attack. Again he made a complete recovery.