Vincent Kartheiser, photographed by Carlos Serrao. Styling by Warren Alfie Baker for Margaret Maldonado; Grooming by Louise Moon. Shirt by Viktor & Rolf. Photo: Carlos Serrao/New York Magazine

Mad Men’s sixth season was a disastrous one for Pete Campbell, Sterling Cooper & Partners’ charmingly smarmy advertising-accounts executive—which made it a great one for Vincent Kartheiser, who plays him. In the span of 13 episodes, Pete got thrown out of the house by his wife, Trudy, for cheating; ran into his father-in-law at a brothel, costing SC&P the $9 million Vicks Chemical account; got banished to the firm’s nascent Los Angeles office; and tangled with a sociopathic co-worker, Bob Benson, who stole the Chevy account from him and may have played a role in the murder of Pete’s mother.

Pete has never been easy to like, but Kartheiser’s exasperated reactions to every setback have launched a thousand gifs and transformed a once-loathsome character into an oddly endearing one. All of which seems to have only inflamed Mad Men creator Matthew Weiner’s sadistic tendencies: “When you put him in positions to be wronged,” Weiner says, “you know you’re gonna get a full Jack Lemmon kind of frustration and anger that’s very physical, very funny.” Like the time, also last season, when, during an argument with his nemesis, Don Draper (Jon Hamm), Pete fell on his ass down a flight of stairs. “It was amazing,” says Weiner. “That was one of the payoffs to spending all that money building that staircase. We knew he would just be apoplectic.”

“It’s a standing joke on our set that I only do outraged,” Kartheiser says. “It’s really the only emotion I can do.”

He gives me a demonstration. We’re at the Campbell Apartment, the very Mad Men bar hidden in a corner of Grand Central Terminal that Kartheiser chose because of the name. He lives in Los Angeles but has been staying in Brooklyn with his fiancée, Alexis Bledel, the former Gilmore Girls actress he met two years ago when she guest-starred as Pete’s mistress in season five. He’d planned to bring his suitcase to the bar and then take a train to New Hampshire to visit his older brother, Nathan, who’s a baker. But he scratched that after hearing that the Campbell Apartment doesn’t allow luggage and wore a jacket and uncomfortable brown leather shoes in deference to the strict dress code. He looks around the room in mock annoyance, probably mixed with a little of the real thing: We’re seated next to a woman in Uggs who’s brought a duffel bag. “So I had to put these shoes on because I read there was a dress code, and that if you have tennis shoes you won’t get in—and look at all these bags and fucking boots! I could’ve been ready for New Hampshire, and now instead I gotta go all the way across town, pick that shit up, and come back to Grand Central. Goddamn it!” He laughs it off, but no sooner have we ordered our cocktails than he’s complaining again: “Man, I was just in Montana,” he says, “and it was $2 for a shot, plus you got a free beer.”

Still, Vincent Kartheiser is not Pete Campbell. Most immediately, there is Kartheiser’s hairline, which is covered in stubble where he shaved bald spots to play Pete, whose scalp can’t even catch a break. And outside of swanky bars, and the ’60s-period clothing he wears on the show, Kartheiser says, “I still dress like I did in high school. My fiancée bought me all of this. She’s like, ‘Honestly, another ripped T-shirt? Put this on.’ ” Then there’s his very un-Pete-like environmentalist lifestyle. Kartheiser is known for being a bit of an ascetic, and extreme in his ecoconsciousness, though it’s sometimes hard to tell the truth from stuff he made up because he was bored in interviews. For example, he does live in a tiny, 580-square-foot cabin in Hollywood, but, contrary to a popular rumor (that Kartheiser started), he has never lived without a toilet. He did, however, spend four years commuting to Mad Men’s L.A. set without a car before he broke down and bought a Volkswagen Golf. “I was just spending a lot of time waiting for buses,” he says.

Kartheiser passed mostly unrecognized on those buses; he was an unknown before Mad Men, even though he’s been acting for nearly 30 years. His first professional gig came at age 7, when he starred as Tiny Tim at the Guthrie Theater in his hometown of Minneapolis. Soon, he was a Guthrie regular and honing his craft at home, too. His parents didn’t buy a TV until he was 10, so instead he and his siblings put on plays, for which his four older sisters made him wear dresses and makeup. “I was almost always a girl,” he says. “I played Molly in Annie—‘Oh my goodness! Oh my goodness!’ ” Because his sisters took the lead roles, “I was never the star, and that was a good lesson for me. Growing up, I learned to support other actors, not to try to steal a scene but to serve the story first.”

By 14, he was making regular trips to Los Angeles for small parts in movies like The Indian in the Cupboard. At 18, he moved there on his own, running amok for a time. “On a scale of one to ten—let’s say ten is John Belushi and one is Jesus—I was a five,” Kartheiser says of that period. He looked like a young Michael Pitt, ethereal and lanky with long, greasy hair, and was cast as a teen drug addict in Larry Clark’s 1998 drama Another Day in Paradise. His only recurring pre–Mad Men TV role was a stint as the superhuman son of David Boreanaz’s titular vampire on Angel.

Weiner auditioned dozens of Petes before finding Kartheiser. The actors read a scene from the pilot in which Pete tells new secretary Peggy (Elisabeth Moss), “If you pull your waist in a little bit, you might look like a woman.” “To both criticize her and flirt with her at the same time was very difficult,” says Weiner. “There was a disinterested, low-energy, snotty, sort of frat-boy thing going on [with the other auditionees]. No skills of seduction whatsoever. Then Vinnie came in, and he just had it all. He was funny, handsome, and felt like a guy who was younger than Don, and hungry. He really popped. You could see a whole person there.”

Kartheiser turned 26 during the filming of the pilot (he’s 34 now), and Weiner decided to make Pete the same age so they’d mature together. Early on, Kartheiser was infamous on the set for doing loud vocal warm-ups before takes. “He would go, ‘Ta-ta-ta-ta-ta, ka-ka-ka-ka-ka.’ He’d start yelling and screaming, and it was a little jarring at first,” says John Slattery, who plays Roger Sterling. “It would be two o’clock in the morning, and you’d be like, ‘Will this guy ever shut the fuck up?’ Then you’d realize that it’s all part of his process, and he’s not just doing it to get attention.” Says Hamm, “We’ve all made our peace with Vinnie’s antics. It’s crossed out of annoying and landed into adorable.”

Photo: Carlos Serrao. Photo: Carlos Serrao/New York Magazine

At the beginning of Mad Men’s seventh and final season (which AMC has split into two halves; the first is on now, and the second will air in 2015), Pete seems to have found some peace of his own in Los Angeles. “The city is flat and ugly, and the air is brown,” he tells Don, “but I love the vibrations.” The new hippieish Pete has traded suits for plaid pants and polo shirts, has a hot new girlfriend, and is landing big accounts again. “A lot of the show plays on the tension of whether people can change or not,” says Weiner. “Pete Campbell has changed the most to me, even more than Peggy.” But it wouldn’t be Mad Men if things went Pete’s way for too long. “I think Pete has more dysfunction than Los Angeles can save him from in the long run,” warns Slattery.

In any case, Kartheiser’s feeling more mellow himself. “A lot happens to a man between 25 and 35. Your testosterone levels drop significantly, so everything’s a bit more relaxed for me,” he says. Finally gone is the fear of being written off the show, as many characters have been, because there aren’t that many episodes left. “There have been certain seasons where I went through insecurities: Oh, they’re not happy with my work, I won’t make it to the end of the season. But now I’m at peace with it. I’m ready to die.” (We know Pete survives at least the first half of the season; after New Hampshire, he’s headed back to L.A. to shoot more episodes.)

Kartheiser isn’t sweating his post–Mad Men career either. Unlike Pete, he says, “I have no ambition. I’ve learned not to have any expectations or any hopes.” During hiatuses from the show, he’s acted in plays (last summer he played Mr. Darcy at the Guthrie) and in indie movies, though none have made any waves. “I think some of them have already come out on iTunes and no one’s watched them,” he says, “and the other ones are pretty well dead in the water. The truth is, I hope I can always just do regional theater somewhere. I don’t have this big fear of ‘Will I ever do something as amazing as Mad Men again?’ because that’s not up to me. And if I put that pressure on myself, how does that help?”

The check for our drinks arrives and Kartheiser turns it over. “Thirty-four dollars and 57 motherfucking cents?!” he shouts. When we get to the coat check, I can’t find my ticket, so the woman guarding my jacket holds it hostage. “Now I want to take back the dollar I tipped her,” he whispers. “Can I dig through your purse? Why don’t you let me hold some stuff? Relax. Everything you pull out I will hold, okay?” To lighten the mood, Kartheiser tap-dances. When we locate the ticket, he sings, “I’ve got a golden ticket!” and hands it over with a flourish before helping me reload everything into my bag. “You are a mess!” he says.

He smokes a cigarette as soon as we get outside, and in a few minutes, he’ll tap-dance again on a subway platform when he realizes that we’ve accidentally stolen our waitress’s pen. “You know what you call this?” he says. “This is the $38 pen. Because you paid $38 for drinks!”

I ask what he did today, before meeting me. “It’s really hard to say,” he says. I press him, and he blurts out, “I had a colonoscopy!” For real? “No,” he says, laughing. “But what if I had? It was a day of personal errands. All really personal shit.”

The shit he’s most protective of is his relationship with Bledel. They had several love scenes on Mad Men, but Kartheiser insists they didn’t start dating until two months after season five had wrapped: “We were completely professional. We never saw each other out. We never—it was nothing, it was just work.”

His co-workers say they all saw it coming, though. “I did know he liked her from a very early point,” says Hamm. “I was a supporter of that union.” Weiner won’t quite take credit for fixing them up. But he says, “I told Vinnie that they would be great together. I was like, ‘Don’t blow it!’ ” He even told the show’s writers that the two would get married. “Honestly, they’re a really good match,” Weiner says. “They’re both very down to earth, with a sense of responsibility and strong family ties. And they’ve been acting since before they can remember, which makes for a very special personality. It’s not just that I thought they would look cute together.” But, he says, laughing, “even with all of Alexis’s amazing qualities, I think that if she had not been such a good actress, he would not have been interested.”

Kartheiser and Bledel have kept a low profile, but they’re beginning to get a sense of what it means to be a celebrity couple. Last May, a British tabloid published paparazzi photos of them relaxing on a Hawaiian beach, with an article claiming that Kartheiser “gave onlookers a rare glance at his muscular chest and biceps.” “Right,” he says, “and all the comments were about what a fat whale I was, and what the hell was she doing with me?” He usually doesn’t read internet comments, but “for something like that, I couldn’t resist.” He says he doesn’t mind, though; it’s a part of the job. “We provide this service which is, you know, being trampled under the feet of society.” He thinks people need to hate on celebrities—and maybe TV characters, too—to feel better about themselves. “We can take it,” he says. “So if it’s worth your time, and it helps you to log in and say something nasty, then I’m happy that I could be there for that.”

*This article appears in the April 21, 2014 issue of New York Magazine.