Mark Sheppard is known for his roles in a number of sci-fi television shows, but for “Supernatural” fans, he is simply Crowley. The 49-year-old English actor has opened up about his role as the King of Hell in The CW series, admitting that even after five seasons, he’s still not certain what Crowley is.

In an exclusive interview with Blastr, Sheppard revealed that he loves playing Crowley, a demon who is sometimes useful to the Winchester brothers Sam and Dean (played by Jared Padalecki and Jensen Ackles respectively) and the angel Castiel (Misha Collins).

And he’s had a long journey from being a high-ranking Crossroads demon to becoming the King of Hell when Lucifer got trapped in the pit.

“Crowley’s been a very interesting evolution. I mean, he went from being what is apparently a crossroads demon to running Hell and then to having difficulties running Hell and then ultimately to be in exile. He’s trying to regain his position. It’s just a fantastic arc to play,” he said.

Spoiler alert! For those who haven’t watched the most recent episode, “King of the Damned,” don’t read the following line.

Crowley’s main rival, Abaddon (Alaina Huffman), has died after Dean killed her with the legendary blade, allowing Crowley to regain his position as the King of Hell.

Sheppard credited the writers for making Crowley one of the most interesting and beloved characters in the show. Executive producer/writer Ben Edlund created the character, which was supposed to last for a few episodes only after first appearing in season five.

However, as it happened, Crowley survived season five, and is still alive today.

“The writers write Crowley so well. It’s so much fun to do, so I think it endures,” he said. “Over the years, I think the stories are getting better. I think writing is fantastic, and I think the fans are a huge part of that. I mean, look at ‘Supernatural.’ We’re in season nine and moving forward into season 10, and I think the stories are getting better. The show is more popular. It’s just been a fantastic year.”

Sheppard has been in many other television series, but his “Supernatural” gig is his longest to date.

“While I’ve had a lot of fun on a lot of other shows, the stories have tended to be of less duration. So Crowley, I’ve done, what, 30 episodes or so by now? It’s over five seasons. It’s a long time. It’s a lovely journey to take.”

But even with “over five seasons” in the show, Sheppard still can’t answer for sure how to describe Crowley.

“I’m still not 100 per cent certain what Crowley is,” he continued. “Crowley could be certainly more than the sum of his parts, I would hope. I think we’re sort of uncovering more of Crowley as we go along. Especially in season nine.”

Thanks to the show’s “incredibly intelligent fanbase,” as Sheppard has described the “Supernatural” fans, the series has now surpassed the life of many other shows.

“Supernatural” season nine ends on May 20.

Read Sheppard’s full interview here.