Vincent Kartheiser

As he goes from slimy Madison Avenue ad exec to tortured post-9/11 artist, Vincent Kartheiser’s steely blue eyes and baby face completely transform from one role to the next.

The 33-year-old actor seems to puff up with pomposity as smarmy ad man Pete Campbell in AMC’s Emmy-winning "Mad Men." But he can also radiate innocence, as he did as wayward son Connor on "Angel" (the Joss Whedon spinoff from "Buffy the Vampire Slayer") and lose himself in a scruffy beard as the agoraphobic novelist Sebastian Justice in "The Death of the Novel," which will make its world premiere Aug. 30 at the San Jose Rep.

Shape-shifting is all in a day’s work for the actor. The youngest of six children, Kartheiser, who was brought up in Minnesota, always has relished being the center of attention. He sang in a choir as a boy, made his stage debut at age 6 as Tiny Tim in "A Christmas Carol" and trained at the prestigious Guthrie Theater in Minneapolis. The craft of acting has been his life for as long as he can remember, but right now he’s smitten by the antihero he plays in "The Death of the Novel," Jonathan Marc Feldman’s bold new stage work.

"I’m so Sebastian right now," he quips, lounging on the set of "Death," which launches San Jose Rep’s fall season and continues through Sept. 23. "Actually, he’s smarter than me and more sensitive than me. He’s cynical and snide because what he is hiding is so delicate and precious. Underneath all his darkness, he has a thread of hope."

Sebastian is an explosive young writer who published one brilliant book before losing his tether on life. Cloistered in his New York apartment, he rants about everything from tennis to global warming, but he can’t seem to do anything — especially write. When his publisher sends over a shrink to get to the bottom of Sebastian’s writer’s block, he discovers a well of grief and inertia deeper than he could have suspected. Mystery shrouds the writer and his demons, as the audience wonders if Sebastian will ever leave the house. Tormented by a volcanic temperament, he runs the risk of being consumed by his own fire.

The thoughtful, soft-spoken Kartheiser, who in real life barely resembles his TV persona, finds Sebastian’s disorders quite compelling.

"How do you live in a world like this one and not go crazy?" he muses, surveying the set for Sebastian’s posh but small Manhattan pad, which has become both sanctuary and cage.

Plunging into a role as deep and dark as this one has taken a toll on the actor, who gives off little hints of fire under a generally sunny surface.

"I am an artist of emotion," he says, his voice thick with feeling. "It’s hard, but it’s also incredibly cathartic. You go to that dark place, and then you get to let it go and go home. It’s a pleasure to inhabit a role like this fully, just like it’s a pleasure to be dishonorable under Pete’s armor (on "Mad Men"). It’s like therapy, only faster."

Speed is part and parcel of the actor’s rigorous work ethic. He is doing "Death" as well as shooting the indie film "Beach Pillows" during a hiatus from "Mad Men," because "two weeks off is all you need."

For the record, no matter what he is doing, Kartheiser finds it hard to escape from Pete. Everywhere he goes, people want the dish on his scheming alter ego, not to mention his rumored romance with Alexis Bledel (late of "Gilmore Girls"), who plays the woman with whom he has a fling on the show.

He shrugs off that kind of fawning. He’s no prima donna; he pads around barefooted, putting away the props after rehearsals, and calls a fellow actor "dudearonomus." He asks other actors to call him Vinny (he was named after St. Vincent de Paul) and bends over backward to give a photographer a good shot.

"I’m not the star," he says. "We’re just a group of people all very engaged with each other, trying to make this work, because it is a play that demands it," he says. "You have to put in that level of effort because the subject matter is very difficult."

Still, part of Kartheiser’s appeal as an actor is the fact that he’s got a little edge under his affability. That flash in this eyes gives his performances heat. He can explode inside a role with uncanny realism.

A ’dangerous’ actor

"It was great watching Vincent step into Sebastian’s shoes," says San Jose Rep artistic director Rick Lombardo. "He is a very intense, focused, intelligent and yet unpredictable and dangerous actor — exactly the type I love to work with. The role fits Vincent like a glove. ... This is the type of work I always gravitate toward — provocative, unyielding, witty and, ultimately, deeply human."

Humanity’s dark side is one of the actor’s sweet spots. Kartheiser says he finds the sleazy ad man Pete easily relatable because the character’s flaws may be reprehensible, but they are also universal.

"I’ve known guilt, shame, impatience, petulance, cruelty," he says. "It’s not always flattering, but it is very human. The people who don’t like the show, because they think the characters are awful, haven’t looked in the mirror very hard."

Indeed, the actor has become so closely associated with the character he plays on "Mad Men" that some fans project their antipathy for Pete onto him. He had to stop taking the bus in Los Angeles because he kept stopping traffic. A couple at a club once bemoaned his presence on the dance floor because they hate Pete Campbell so much.

’Mad’ fame

If playing the villain means dealing with insane fan reactions, he’s still grateful for the fame "Mad Men" has brought him.

"It means I get to ... champion projects like this one," he says. "From the first moment I read the script, I knew this was something I wanted to do. It’s genius."

The play’s pungent social critique and damning examination of social media, the loss of privacy and the rise of anonymity speak to him. "I’m inspired by this play, which is concerned with the world that we live in right now, a world where we are hyperconnected but also so detached from each other, it’s spooky."

Although Kartheiser has been away from the stage for seven years, he has never lost his taste for it. He counts "Mad Men" as the most fun he has ever had as an actor, but he admits he misses the rigors and riskiness of live performance. Once he has "Death" on its feet, he hopes to take a crack at Wallace Shawn’s blistering solo show "The Fever," a commentary on the evils of global consumerism.

"There’s nothing like having an audience right there in front of you, breathing with you, living with you," he says. "That’s what feeds me as an actor. I want to have it all on the line."