The earliest known mention of Spock was in a conversation between Star Treks creator Gene Roddenberry and actor Gary Lockwood, in which Lockwood suggested Leonard Nimoy for the role. The trio had previously worked together on Roddenberry's The Lieutenant in the episode "In the Highest Tradition". Roddenberry agreed to the idea, but was required to audition other actors for the part. At the time, Roddenberry sought DeForest Kelley to play the doctor character in the pilot, "The Cage", but both NBC executives and director Robert Butler wanted Kelley to play Spock. Roddenberry offered the part to both Kelley and Martin Landau, but they both turned him down. When offered, Nimoy accepted the part but was apprehensive about the make-up which had not been determined at that point.
