He's the youngest cast member, but he plays the oldest character. He's also built up to new shirtless measurements. He's Jason Dohring, and he's back on television tonight, as a vampire in "Moonlight."

Dohring, 25, took over the role of the 400-year-old vampire who sired "Moonlight's" lead character Mick St. John, from a 60-year-old actor who appeared in the show's original pilot. Best known as the bad boy-sometimes-boyfriend of Veronica Mars, Dohring easily won the role, partly because both "Veronica Mars" and "Moonlight" share Hollywood mogul Joel Silver as their executive producer.

He also had the advantage of auditioning for David Greenwalt, co-creator of "Angel," did some major overhaul on "Moonlight" in the brief time he worked as showrunner before he left for health reasons. Greenwalt essentially recast the entire show, with the exception of the of St. John, who is played by Alex O'Loughlin.

"It was really cool that [Joel] called out of the blue and said, 'There's a role, and I'm making it younger'," Dohring said in a July interview. "I read the two pages that they had. It's such a dark character. He was sharp. I was like, 'I get this guy. I get it.'"

Comparing his "Veronica Mars" character and the vampire Josef, Dohring said
"This character is like Logan but even more extreme, which is fun to play. It's cool to keep going forward in challenges, as opposed to doing something you've done before. This is not like what I've done before. There's no little blonde girl, just a tall, dark, handsome drink of water."

"That's going to take some acting," Dohring said, "especially with Alex. That's the challenge right there, for me, keeping that there. But at the same time, Mick's more of a moral character, so there's some respect there in that regard, because I'm without that quality, the moral-ness."

Since "Veronica Mars," Dohring has worked to build up his physique. "I actually got a little too big," he said, "because I couldn't move around as much as I wanted to. When you get muscled, it actually resists flexibility, so I'm doing stretching, working out with just my own weight, not the huge weights, but push-ups and pull-ups."

Dohring, who will most likely be seen shirtless at least once in the series, also gets to show off his new physique with some very distinctive clothing.

"When I came in for my first fitting," he said, "it was Versace and Armani. There was nothing that wasn't high end."

"Moonlight" premieres tonight on CBS, and airs Fridays at 9 p.m. ET.