Cobie Smulders, Kal Penn

As far as typecasting goes, Kal Penn fills some very specific criteria.

"This is the third doctor character with a name that starts with 'K,'" he tells TVGuide.com of his How I Met Your Mother therapist Kevin. His previous — and most famous — two roles, of course, were Kumar of the Harold & Kumar movies and the late Dr. Kutner on House. "You find out [in the upcoming A Very Harold & Kumar Christmas] that Kumar actually completed med school in the six years that have been left off," Penn says. "I think it was a buddy of mine who asked me, 'What were the last few characters you played?' I said, 'Well, I just went back to play Kumar and I guess Kutner killed himself off and now I'm playing Kevin.' And I was like, 'Whoa!'" My name starts with 'K,' so maybe it's something subconscious."

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Whether or not he's cornered the market on doctors with "K" names roles, Penn is excited to be acting again after leaving House in 2009 to join the White House Office of Public Engagement as associate director. His plan was always to stay at the post for two years (save for five months he took off to film A Very Harold & Kumar Christmas) and then return to showbiz. It just so happened that Mother — with Harold & Kumar cohort Neil Patrick Harris — was searching for a love interest for Robin (Cobie Smulders) at the same time. "I love the show, so it was perfect," Penn says. "I had also worked with Alyson [Hannigan] briefly, like way back in the day I did an episode of Buffy the Vampire Slayer and she was great to work with. ... I said I would love to do it if they would like to have me."

The actor is currently signed on for eight episodes as Robin's new beau and court-mandated shrink — a result of her assaulting a chick pursuing Barney (Harris). While Kevin's tough-love style last week hardly seems like he's into Robin, that will all change on Monday's episode when he and Robin bump into each other outside of the office.

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"The sparks start. You saw the guy in the suit; now you see the guy in jeans. And he meets her friends. Much like a lot of people, there's the professional etiquette and then there's the personal etiquette, which are often times different," Penn says. "It's probably also a little bit of like seeing your fourth-grade teacher in the grocery store for the first time and realizing she's not just your fourth-grade teacher. She has this whole other life and it's a little weird. It's an equivalent of that."

It's also weird because, well, he's her therapist. On the other hand, there is something to be said about being forced to open up to someone. "Here's this guy who connects with her and understands her in a way no one has before," Penn says. "I don't think either of them was expecting to fall for each other. The attraction definitely catches both of them off guard, so they do tackle some of those questions. But for him, he finds her very attractive with a very funny personality. I guess the same for her. He wasn't terribly sympathetic at first because her [assault] back story is not nearly as bizarre as some of the [stories] he's used to. He's used to treating disturbed felons. But he's got his quirks too. What you learn this week is that he's a layered guy."

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The big question is: Will Kevin be the guy who helps Robin move on from a very not single Barney? Penn, who's developing a sitcom for NBC, doesn't know — mostly because Kevin doesn't know about Robin and Barney's complicated history yet.

"We just did the table read for the fourth episode that I'm in ... and Kevin still doesn't know," he says. "She hasn't yet opened up about that. I suppose they have to address it at some point. I think Kevin would assume that she's dated other people. I don't know that he would assume some of them would be people she hangs out with every day, and one who is Barney!"

But if Penn had his druthers, Kevin would be exactly what the doctor ordered for Robin. "I'm biased, so I hope she stays with Kevin! ... I'm only doing these eight [episodes] now, but I'd love to do more," he says. "They're a fun couple, a fun match. You'll see that. ... There's inevitably a difference between understanding someone as a therapist and as a boyfriend, but she needs someone to hear her out right now, and he's doing that for her."

How I Met Your Mother airs Mondays at 8/7c on CBS.