Kelley became a good friend of "Star Trek" castmates William Shatner and Leonard Nimoy, from their first meeting in 1964. During "Trek"'s first season, Kelley's name was listed in the end credits along with the rest of the cast. Only Shatner and Nimoy were listed in the opening credits. As Kelley's role grew in importance during the first season, he received a pay raise to about $2,500 per episode and received third billing starting in the second season after Nimoy. Despite the show's recognition of Kelley as one of its stars, he was frustrated by the greater attention that Shatner received as its lead actor and that Nimoy received because of "Spockamania" among fans.