Early life and education
Robertson was born in La Jolla, California, the son of Clifford Parker Robertson Jr. (1902–1968), and his first wife, Audrey Olga Robertson (née Willingham; 1903–1925). His Texas-born father was described as "the idle heir to a tidy sum of ranching money". Robertson once said, "[My father] was a very romantic figure – tall, handsome. He married four or five times, and between marriages he'd pop in to see me. He was a great raconteur, and he was always surrounded by sycophants who let him pick up the tab. During the Great Depression, he tapped the trust for $500,000, and six months later he was back for more."
Robertson's parents divorced when he was one, and his mother died of peritonitis a year later in El Paso, Texas, at the age of 21. He was raised by his maternal grandmother, Mary Eleanor "Eleanora" Willingham (née Sawyer, 1875–1957), in California, and rarely saw his father. He graduated in 1941 from La Jolla High School, where he was known as "The Walking Phoenix".
He served in the U.S. Merchant Marine in World War II, before attending Antioch College in Yellow Springs, Ohio, and dropping out to work as a journalist for a short time.