Cobie Smulders, Kal Penn 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 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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