It was first announced in July that the former Lost and Supernatural star will play the vampire Bishop in the show.
He told Daemon's TV: "Bishop is a very old vampire. He was turned in the 1600s in England [and] came over to the New World because of the Revolutionary War to make his bones and his mark in the world. He has become the vampire boss of Boston."
Pellgrino confirmed that Bishop is responsible for turning Aidan (Sam Witwer) into a vampire.
"Aidan has since had second thoughts about his lifestyle and is trying desperately to change it," he explained. "I'm trying desperately to bring him back in the fold."
The actor also claimed that his character is not an "archetypal" villain.
"I'm supposed to be villainous, I guess, but you can relate to me," he said. "You understand what I'm going through and hopefully empathise with my point of view. I think everybody [in the show] has those moments of grey."
Being Human begins on January 17 at 9/8c on Syfy.