Nathan Fillion Was Noted for Acting Too Much Like ‘Castle’ in ‘The Rookie’

Actor Nathan Fillion had just wrapped up his role in “Castle” when he transitioned to “The Rookie.” Despite this, Fillion acknowledged the challenge of distancing himself from his character, Richard Castle, while engaging in his new role on another ABC series.

Fillion’s adjustment to “The Rookie” may have been gradual as he found himself in somewhat familiar territory—like Castle, his character John Nolan was involved in crime-solving. This similarity sometimes made it easy for elements of Rick Castle to emerge during performances, even post-“Castle.”

In terms of personality, however, Castle and Nolan were distinctly different. Rick Castle was portrayed as a mystery writer who often joined police investigations, initially for amusement. His approach to the grim realities of crime was frequently light-hearted, infused with humor.

“He kind of started off as this womanizing playboy, but success just comes easy to him,” Fillion explained in an interview with Oprah. “He’s well-liked, very playful—women find him appealing. He’s joyful, somewhat childlike, maybe even displaying a bit of Peter Pan syndrome; he’s never really grown up, partly due to the lack of a male adult role model in his life. He’s always surrounded by women and struggles with how to behave like an adult.”

On the other hand, John Nolan is depicted as an average middle-aged man who aspires to impact lives positively by becoming a police officer—a role requiring a serious commitment to his duties. This stark contrast in character profiles made it essential for showrunners to prevent any overlapping mannerisms between Castle and Nolan.

“There are times when my executive producer would tell me, ‘That was great, but it’s a little too Castle; you might want to dial it back,'” Fillion shared with Entertainment Tonight. “After eight years, it’s challenging not to slip into Castle’s habits.”

Fillion believed that what set “Castle” apart from other police procedural dramas was its light-hearted approach to crime-solving.

“People like me watch crime dramas and think, ‘That would have been a great spot for a joke,'” Fillion remarked to MytakeonTV. “On Castle, we didn’t hold back on the humor. We aimed to capture the lighter side of life, even in a setting driven by dark, haunting events.”

Fillion also reflected on the blend of humor and gravity in the series, recalling his interactions with homicide detectives while filming “Castle’s” pilot in New York.

“These homicide detectives weren’t brooding or haunted by their work; they were actually quite humorous and relaxed,” Fillion recalled in an interview with Hitflix (via Hypable). “Their stories always began with, ‘So this guy gets killed…’ but their demeanor was light-hearted.”

Ultimately, the show’s darker themes facilitated necessary character development, enabling Castle to mature in response to serious life events.

“Like anyone, people need to grow,” Fillion noted. “Castle might be a child at heart, but as an adult, he faces real challenges, which is very much like real life.”