Dr. Thomas "Tom" Leighton was a male Human civilian in the 23rd century. He was an empirical research scientist; Spock, who knew of him, described him to Kirk as "steady, reputable, occasionally brilliant." In 2266, he lived with his wife, Martha Leighton, on Planet Q.
In 2246, he was living on Tarsus IV when four thousand people were executed on the orders of Governor Kodos. Leighton was one of nine eyewitnesses who could identify the governor on sight. Leighton and Kirk appeared to have been personal acquaintances, perhaps as a result of their shared experiences on Tarsus IV. He was tormented by what happened that day for the next twenty years.
In 2266, Leighton diverted the USS Enterprise to Planet Q, ostensibly to confirm his discovery of a new synthetic food that could totally end the threat of famine on Cygnia Minor, a nearby colony. In fact, he diverted the Enterprise because he believed that Anton Karidian, a traveling performer, was actually Kodos. He hoped Kirk, another of the eyewitnesses, would help him in his quest to bring Kodos to justice. Kirk wasn't convinced until, ironically, Leighton was found dead. Lenore Karidian, insanely desperate to protect her father from his past, had murdered Leighton; he was the seventh victim of her quest to eliminate all those who could identify Kodos. Leighton was survived by his wife Martha. (TOS: "The Conscience of the King")
Background information Edit
Thomas Leighton was portrayed by William Sargent.
In the final revised draft script of "The Conscience of the King", Dr. Leighton was initially described merely as "a contemporary of Kirk's."
Although it was not explicitly stated, conversational context strongly suggested that the left side of Leighton's face was ruined during the massacre at Tarsus IV. The script didn't specify this injury, merely referring to Leighton having a "crippled body" instead. In a deleted scene from "The Conscience of the King", Leighton was established as having lost his parents and two brothers during the massacre, and having experienced, ever since then, nightmares about the incident. ("Swept Up: Snippets from the Cutting Room Floor", Star Trek: The Original Series - The Roddenberry Vault special features) Later in the script, upon Kirk breaking the news to Spock that there hadn't actually been any synthetic food samples and Spock replying that would need to be noted due to the seriousness of diverting a starship, Kirk remarked, "Well, a black mark against Dr. Leighton isn't going to hurt him now."
Who's Who in Star Trek 1 mistakenly calls him Robert Leighton.