He was my favorite character in the show. I can't decide when Sliders started it's dismal journey into hell in a hand basket... it was either with the death of the prof, or with that whole (i forget the name of that Nazi-like sliding alien race...) storyline.
I liked that actor in other films such as 'Raiders of the Lost Ark' too.
He played the hologram of Leonardo on more than one episode, and I'm not sure what season, but I thought it was the second to last, or the one before that. I was hoping he would be a regular, but no such luck. What was great about the charactor was that he had a love of science and adventure, which was so like the professor.