‘Castle’ may be over, but Nathan Fillion is back on ABC as ‘The Rookie’

As a young boy growing up in Canada, Nathan Fillion spent many a day playing cops and robbers with his older brother. Actually, they played Highway Patrol officers. If we’re being super specific, they pretended to be the leads of TV’s late-’70s classic “CHiPs.”

Fillion, as the fairer-haired brother, took on the role of Jon Baker, opposite his brother’s turn as Frank “Ponch” Poncherello. “We’d be on our bikes with walkie-talkies that were terrible and never worked,” Fillion recalls with the smirk of a man with hindsight.

These days, Fillion, now 47, has graduated to playing a rookie police officer.

Two years after wrapping his stint on ABC’s popular whodunit procedural “Castle,” Fillion returns to the network in the new cop drama “The Rookie.” Based on a true story, the series follows John Nolan (Fillion), a 40-year-old, recently divorced small-town guy who, after a life-changing incident, decides to leave his comfortable life to pursue a career as a cop — becoming the oldest rookie officer in Los Angeles Police Department history. The series premieres Oct. 16.

Inside a spacious trailer on the Warner Bros. lot in Burbank, Fillion, who also serves as an executive producer on the series, has plopped down in a chair during an afternoon break from filming the fifth episode of the season. He’s as genial and self-deprecating as you’d expect from a guy whose earned the reputation as the charming guy-next-door. He also has that slightly tired-but-resilient look of a person settling back into the grind of a network hour-long drama.

“I had my doubts as to whether or not I was ready to come back to work,” says Fillion, who had an eight-season run as a cheeky crime solver in “Castle.” “All the way up to the first day. But that log line for the show — it had me from the start.”

Specifically, this idea of hitting the reset button later in life felt to Fillion like intriguing ground to cover.

“This is the new norm, starting over,” he says. “It used to be that you get a job and that’s your job until you retire. Things move much faster now. Things change so rapidly in our society. You have to change with it or you get left behind. It’s amazing to me to see anybody take life by the horns and say, ‘I’m gonna do this.’ It’s courageous.”

Fillion knows something about changing course. He was raised by two English teachers, and like his brother, was on the path to become an educator.

“I didn’t have a passion for teaching, by any means,” he says. “I wanted to act, I like creating things. So, I figured I’d be an art or drama teacher. I thought I could still pursue passions, things I’d enjoy, while also having a pension and a retirement and summers off. I told my parents my plan: ‘I’m going to get my degree, and then I’m going to go try acting. I’m going to go try it. We’ll see what happens. I doubt I’ll succeed, I’m sure it’ll be tough, it’s terrible, it’s not so good, but I can always fall back on teaching.’”

Needless to say, he’s never been Mr. Fillion in a classroom setting. His Edmonton theater work led to a role on the soap opera, “One Life to Live,” in 1994. Of course, he could certainly teach a course in the art of building a career as a reliable prime-time television star who also has rock star-like status at Comic-Con with an impressive résumé of cult-following projects (Joss Whedon’s “Firefly,” “Dr. Horrible’s Sing-Along Blog” or James Gunn’s “Super”).

“He’s really a dream to write for because he can do anything,” said “The Rookie” creator Alexi Hawley, who previously worked with Fillion on “Castle.” “On a personal level, he’s an incredibly charming, very genuine guy. That second part is what you don’t always get in Hollywood. There’s plenty of charming people here, but there’s not a lot of depth to it. But with Nathan, he really is just a kind-hearted, good guy.”

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“The Rookie” further deepens Fillion’s ties to ABC. He scored his break on the network’s comedy series, “Two Guys and a Girl” before transitioning on to “Firefly” and “Castle” — he’s also had roles on “Desperate Housewives” and “Modern Family.”

“What I think the audiences respond to with Nathan is he feels very accessible,” said ABC Entertainment President Channing Dungey. “Yet, at the same time, he’s heroic. He’s like the guy-next-door gone one degree better. I think that’s what makes him relatable but also grounded. I think that’s a big part of his appeal with audiences.”

As Fillion tells it, he’s “super-duper lucky” to have portrayed a lot of characters that appeal to him.

“Even if they’re not particularly nice characters, they’re so flawed that you like to judge them,” Fillion says. “There’s a safety in judging. It’s like, ‘I’m glad I’m not that guy. I know I’m smarter than this guy. That guy, he’s so flawed.’ That it makes you feel better about yourself watching someone who’s terribly flawed. If I’ve been pigeonholed as anything, it’s as that likable, for whatever reason, guy. I’m super-fortunate.”

To maintain his grip on the heroic guy-next-door persona this time around requires a finesse with action sequences. The stunt work — however much of it he chooses to do — has already prompted Fillion to come up with his go-to zinger about doing action scenes at this stage in his life.

“I am actually a decrepit,” he says. “I am fond of telling people, ‘Just kneeling down for me is a stunt.’” And he maintains that the trick to not looking like you’re a blob while running on TV is “small steps and high knees.”

Fillion, along with the cast, went through police training where they learned such procedures as how to cuff someone, how to clear a room, how to use nonverbal cues with a partner. Then there was a matter of honing in on the spirit of the middle-age rookie officer on which his character is based. (Producers have chosen not to reveal the officer’s real name.)

“I enjoy talking to him,” Fillion says. “His experience is his unique superpower. Sometimes I think it serves him very, very well. And in other ways, I think it’s a detriment. And I think that’s an interesting dynamic to play.”

So, if ever he experienced his own life-altering event, what would be his do-over?

“I think you can only be relevant for so long,” Fillion says. “I would like to be relevant until I decide to quit, but if the world moves on without me, I think I could teach acting. I think that would be fun to do. I’m not very good at the business aspect of it, so I think guest speaking would be my thing.”

yvonne.villarreal@latimes.com

Twitter: @villarrealy