Nathan Fillion agreed to star in ABC's The Rookie before reading any scripts, drawn by the show's core concept and his prior collaboration with creator Alexi Hawley.
The actor portrays John Nolan, a man in his 40s who joins the Los Angeles Police Department after witnessing a bank robbery. Fillion accepted the role based on the pitch alone during early development discussions with Hawley, who had worked with him on the series Castle from 2009 to 2016. In a 2018 interview, Fillion noted that the idea provided strong potential for long-term storytelling because the character starts his life over from scratch.