The original plans for Leroy Jethro Gibbs in NCIS would have been significantly different if Harrison Ford had been cast in the role. Ford was the creators' initial choice for the character, but the role was eventually given to Mark Harmon. If Ford had been cast, Gibbs would not have been as prominent in the series due to Ford's movie career. This could have negatively impacted the show's storytelling. Additionally, Ford's chemistry with the rest of the cast would have been uncertain, potentially leading to the early end of NCIS. However, ultimately, casting Harmon was the best decision for the show and allowed Ford to continue his successful film career.