Prior to production, United Artists had made it quite clear to director John Sturges that none of the primary roles were to be filled by the actors who played the same characters in Sturges' previous Wyatt Earp film, Gunfight at the O.K. Corral. Wanting to distinguish this film from the previous one, they demanded different actors be cast in the roles. However, Sturges believed that the roles of Virgil and Morgan Earp from the previous film were small enough that the same actors who played them could do it again without harming the film's uniqueness. The studio agreed and allowed Sturges to cast John Hudson (Virgil Earp) and DeForest Kelley (Morgan Earp). Unfortunately, Hudson had retired from acting in the early '60s and was unwilling to do the role. Kelley, on the other hand, was currently working on the TV series Star Trek and was unable to break away to play Morgan Earp. Thus, both Earp brothers were recast.