His family confirmed that the actor passed away on Thursday in Malibu.
Robert was the son of Hollywood stars Robert Walker and Oscar-winning actress Jennifer Jones.
Born April 15, 1940, Robert found fame in a series of TV appearances during the 1960s, including playing teenager Charlie Evans in the original series of Star Trek.
His character also went by the name of Charlie X with his episode being the second ever to broadcast, when it was aired in 1966.
Robert’s episode of the beloved franchise was the second ever to be broadcast, and aired in 1966.
During that episode, the then 26-year-old Robert played a 17-year-old named Charlie X. He was rescued as a castaway after surviving for 14 years amid the wreckage of a transport ship.
He is taken aboard the USS Enterprise but he then becomes a dark force as his mental powers are revealed, putting the crew in danger.
Robert also appeared in the classic counter-culture movie, Easy Rider. He starred alongside Peter Fonda, Dennis Hopper and Jack Nicholson as well as Ellie Wood, who would become the first of his three wives.
His other on-screen include Route 66, Bonanza, The Six Million Dollar Man, Quincy, M.E., Charlie’s Angels, Columbo, L.A. Law, and Murder, She Wrote.
Robert is survived by his wife Dawn and his seven children – Michelle, David, Charlie, Jordan, Colette, Henry and Emily. He also has five grandchildren.
In a statement to The Hollywood Reporter, Robert’s wife said: “Bob always beat to his own drum and stayed true to himself in all of his endeavours.
“Although an accomplished actor, his true art was living fully.
“He was a photographer, drummer, raconteur and gallery owner. His love of the ocean kept him in Malibu, and he had great tales of his adventures paddling to Catalina from there.
“Bob [also] had a constant interest in developing his internal martial arts practice.”