I grew up watching the old Battlestar Galactica episodes on Saturdays and loving every minute. His Apollo character was always the straight hero type. Make no mistake he was the hero of the show more or less. I was a little miffed they wrote (or forgotten) about his character in Galactica 1980. Though it is kind of implied that he was killed off between the two series.
Hatch was in everything in the TV realm during the 70s and 80s. (CHiPs Fantasy Island Murder, She Wrote ) He was in an episode of T.J. Hooker which co-starred William Shatner. Heck, he was in Baywatch.
I know most of the younger people remember him from the newer BSG show. I was never a huge fan of that show, but I liked what I saw of his character. He also wrote a lot of BSG stories based on the old continuity. He kept the franchise alive for many years. He even tried to continue the series with his own proposal series before the Ron Moore series took root (there was another series planned with Bryan Singer).
He was also one of the main stars of the upcoming major fan film Star Trek: Anxar. He plays an important Klingon. I liked his role in the prelude episode. I am guessing he finished the fan movie before his death.
Check out his proposed re-launch of his version of BSG he pitched to the studio.