John Lithgow as a Psychopathic Murderer

Nov. 8, 2009— -- In a storied career that has included roles as aliens, transvestite football players and presidents, John Lithgow finds himself in a part he especially relishes: psychopathic murderer.

As Arthur Mitchell on the Showtime drama Dexter (Sunday, 9 ET/PT), Lithgow is the Trinity Killer, a violent serial murderer responsible for the deaths of 60 people.

"It's been a fantastic experience. I love the fact that he's so nondescript – that makes him all the more terrifying," says Lithgow, who spoke from London after completing a two week run of his acclaimed one-man stage play, Stories by Heart.

Lithgow, 64, wasn't a regular Dexter viewer before he was offered the key role for the drama's fourth season. But Mitchell's complex, layered character and storyline enthralled him. "I was on the edge of my seat," Lithgow says. "It unfolds like a long mystery novel, full of astonishing revelations that have tremendous tension to who (Mitchell) is and what he presents to the world."

Indeed, Lithgow's Mitchell isn't the cut-and-dry villain he seemed in early episodes, when he appeared to be the loner who since-departed FBI profiler Frank Lundy (Keith Carradine) was tracking. Halfway through the season, Mitchell was revealed as a family man, teacher, church deacon and community activist whose Hallmark-card existence masked his extracurricular madness and flashes of violence.

"I love the blandness of both his good and evil side. It makes him scary and creepy," says Lithgow, best known for his double Emmy-winning performance as alien-out-of-water Dick Solomon on 3rd Rock from the Sun.

Lithgow had portrayed killers and psychotics before the NBC sitcom ended its six-season run in 2001, including memorable performances as an escaped con who torments Denzel Washington in 1991's Ricochet and as Sylvester Stallone's foil in 1993's Cliffhanger.

But it's the attention from 3rd Rock– which endures in wide syndication – that has enticed a newer generation of fans.

"The one great thing about having a background in comedy is that it gives you an opportunity to surprise and shock people," Lithgow says. "It's fun to do something people don't expect."