NCIS originally had plans to cast Harrison Ford as Leroy Jethro Gibbs, but Mark Harmon ended up securing the role. The creators thought Ford, a known movie star, would be a perfect fit for the character. However, Harmon's portrayal of a Secret Service agent in The West Wing convinced them otherwise. Additionally, Harmon's commitment to television made him a better choice, as Ford's movie career would have made it difficult for him to dedicate time to the show. Ultimately, Harmon's performance as Gibbs contributed to the success of NCIS.