Nathan Fillion

When Mom tells you you’re a geek, you’re a geek. And that is a badge of honor that actor Nathan Fillion wears proudly.

His mother, Cookie, also has pointed out an advantage that Fillion has: a mainstream look, one that has taken him to a place where he’s adored by the women enamored with his square jaw and boyish smile, and by the men who simply like a guy who knows as much Star Wars trivia as they do.

Soap opera fans picked up on Fillion, who had stints on One Life to Live in the mid-1990s and later on Desperate Housewives. He has become a cult hero for his fellow geeks with such sci-fi fare as the short-lived TV series Firefly and the Web series Dr. Horrible’s Sing-Along Blog. And then there’s the prime-time crowd who associates him with the late-’90s sitcom Two Guys and a Girl and the ABC drama Castle, premiering its third season Monday night.

So how does a geek earn as much mainstream cred as Fillion has? He might be the most taken aback by the situation.

"I’m the luckiest geek you’ll ever meet," Fillion, 39, confides.

At his place in Los Angeles, Fillion stores his collectibles in a large glass cabinet. His eyes light up as he runs down its contents, from the gun and holster he used as Capt. Malcolm Reynolds on Firefly to assorted action figures to his holy grail, a Star Wars light saber. "That’s like my Batcave," he says.

His older brother, Jeff, often comes down from their native Canada to visit, and it’s his sibling whom Fillion channels to play Richard Castle, the best-selling mystery novelist with crime-solving smarts and a lovable overconfidence that excites and exasperates his police partner, Kate Beckett (Stana Katic).

"People are attracted to my brother and they don’t know why," Fillion says. "He’s just good in his heart, doesn’t care what anybody thinks. He’s not trying to be anyone except himself, and that’s Castle."

The brothers were close growing up in Edmonton, Alberta. Their parents were teachers, and Fillion’s dad, Bob, would take the kids to a secondhand book store to buy comic books. (His favorite superhero then? Spider-Man.)

Fillion cared for his comics, bagging and boarding them as he entered his teen years, but that changed.

"Comics were everything. Then it got to the point where, oh, do I spend my money on comic books, or on gas for my car and lunch when I get to school and going to a movie with a girl?" remembers Fillion, who stars as a hero called the Holy Avenger in the dark comedy Super, which just premiered at the Toronto International Film Festival.

Fillion, who was one class short of finishing an education degree when he got the call to be on One Life to Live, visits classrooms to talk with students. Even though he doesn’t have any kids of his own, he likes sharing his geeky interests with youngsters.

"My dad was really cool with me," he says. "I remember watching different things and him helping me understand what was going on.

"I also remember seeing Star Wars for the first time with my dad. I leaned over to him in the theater as it was beginning and said, ’I want to see this again tomorrow.’ And he leaned over and said, ’OK.’ "