Robert Walker Jr. is most frequently remembered for his role on the original series of Star Trek in the episode "Charlie X". Charlie, played by Walker with utter sincerity, is a teenager who has spent the past fourteen years utterly alone after being the sole survivor of a ship crash. He's taken aboard the Enterprise en route for a human colony, and is soon revealed to have reality-bending powers and a vicious dislike of anyone who "doesn't like him". 

"Charlie X" was only the second episode of Star Trek and set the tone for much of the series. It was the only episode that Gene Roddenberry appeared in (uncredited, as a voice exclaiming that his turkey-shaped meatloaf had inexpilcably turned into turkeys). Walker is considered one of the best guest stars on the series and his performance of Charlie as naïve and easily corrupted by power is one that stays with you.

Charlie develops an obsession with Yeoman Rand

Walker also appeared on other classic TV shows. On Bonanza, he played Mark Cole on the episode "The Gentle Ones", about an animal-loving cowboy who must stand up to his older brother. That wasn't the only time he played a cowboy— he played opposite John Wayne in the film The War Wagon.

Walker and John Wayne in Walker and John Wayne in ''The War Wagon''

In 1969 he appeared in the film Easy Rider as one of the hippies living in the commune that Dennis Hopper and Peter Fonda pass through.

The actor was 79 years old when he passed on December 5, 2019.