There’s only one guy we know of who could get mobbed by the hordes at Comic-Con and the moms at Costco: Nathan Fillion. A card-carrying member of the Whedonverse since Firefly debuted (and was canceled) in 2002, his rugged handsomeness and quick wit have been favorite topics of conversation among geeks for nearly a decade. But now, we’re having chats with our 63-year-old mothers about his smile, usually around 11 p.m. on Mondays. How did that happen?

To find out, we stopped by the set of ABC’s Castle this week, woke Fillion from a sound sleep in his trailer (he’d worked all last weekend), and asked the actor starring as crime novelist Richard Castle — who’s partnered with NYPD homicide detective Kate Beckett (Stana Katic) for “book research” — to recount his whereabouts from 1994 to today. What we discovered is, during his rise from soap star to one of primetime’s most popular leading men, Nathan Fillion has never taken a job just for the paycheck. “Everything I’ve done I’ve done with an excitement of ‘I can’t wait to do this!’” he says. It’s because he’s stayed true to who he is — a geek whose advantage is he looks mainstream, as his mother would say — that he’s gone from playing Joss Whedon’s personal Harrison Ford to embodying the TV character EW.com readers have crowned the man they would most like to date. It’s easy for him to have that infectious enthusiasm for characters when there’s so much of him in them. We talked to Castle creator Andrew Marlowe and costar Stana Katic to learn what Fillion and Castle share besides their boyish charm. “He’s a guy who I thought had the many facets to show the many different kinds of faces of what it meant to be a man,” Marlowe says of casting the nearly 40-year-old actor. “To play the beleaguered son, the loving father, a potential love interest who’s charming but someone who is also really annoying yet can get away with it — Nathan had that in spades.” [Read The Rest Here]