U.S. actor Michael C. Hall says he had "no choice" but to take on the role of Dexter Morgan, the serial killer who only targets the bad guys on the popular Showtime drama series, Dexter.

Hall, 41, had previously played the closeted gay man David Fisher on Six Feet Under and found himself again facing the role of a repressed character, with father issues, who play-acts at life.

"It was a kind of open-ended commitment to a character in a world fraught with darkness, but  I had no choice but to do it ultimately," he told CBC’s Q cultural affairs show in an interview aired Thursday.

"It felt like it would be a kind of denial of something not to do it. That would be based on fear of some kind of insidiousness in doing dark material as I have done for over a decade."

Hall said he was unsure of the impact that Dexter would have. By day his character helps uphold the law as a blood-spatter analyst for the Miami Metro Police Department. By night, he's a serial killer with a code, targeting those who violently break the law and get away with it.

Though initially the drama drew criticism for its dicey morality, it became a hit. Dexter is about to wrap up its seventh season this week on TMN in Canada and will run just one more season before wrapping up.

Hall believes nuance has been introduced into the series as it progresses.

"Is he playing at life or is he actually having the experience? I think he made a deal that he wanted to involve in [life], but now he’s not so sure. He’s in a confused place. He is a sad guy because his desire for connection is what ropes him in in a psychological way and literally does in the people closest to him," Hall said.

In his interview with Q, Hall pondered over why people are drawn to the Dexter character.

He said he won’t know until the series is over whether it’s had an impact on his outlook or his career.

But he agreed he feels lighthearted on the days when he’ll be shooting a scene in which Dexter does a killing.

"It lightens my mood — if I’m playing character who 95 per cent of the time is simulating something he’s not, he should feel good when he’s being genuine to himself."

Hall will soon star in the film Kill My Darlings, which is to debut at the Sundance Film Festival.