I grew up on The Greatest American Hero and The Outer Limits (My favorite episode of the latter was Architects of Fear, starring him. In it in a plot very reminiscent of Watchmen he is one of a group of scientists who attempted to fake an alien invasion to scare the world into peace and togetherness.) I loved his roles on those shows. My mom and aunt both had crushes on him.
There was also his voice. It was just so crisp and concise. Even in movies and shows where he had very minor roles such as his part as the President in The Pelican Brief I would know it's him immediately.
He wasn't just a fine actor but a great man. When he starred in I Spy, conservative executives wanted to recast Bill Cosby's role because they didn't want a black man in the part. Culp stood up for his friend and for rights of humans everywhere saying that if they wanted Cosby to leave then he would leave. The executives backed off and because of that act, he helped pave the way for Cosby's fame and for the opportunities for minorities everywhere. He was also heavily involved with other aspects of the civil rights movement, such as when he and Cosby went to Memphis to to join the striking garbage workers Martin Luther King Jr. had been organizing during his assassination.
As a gamer I selfishly just wanted to hear his voice once again
as Dr. Breen. That day may never come. But he didn't just belong to us, but the world. We will miss him dearly.