A scientist who survived the Tarsus IV massacre and urges Kirk to investigate the actor Anton Karidian as the long-missing Kodos.
Dr. Thomas Leighton is one of the few surviving eyewitnesses who saw Governor Kodos during the massacre on Tarsus IV, where thousands of colonists were executed. He carries both physical scars and painful memories from the atrocity.
In The Conscience of the King, Leighton summons Kirk to Planet Q with a story about a new food synthetic, but his real purpose is to show Kirk the touring actor Anton Karidian, whom he believes is Kodos. Before he can testify, Leighton is murdered, the first of several killings that point toward Karidian's daughter Lenore. He was played by William Sargent.