Thann

From Memory Alpha, the free Star Trek reference

Thann was a Vian in the 23rd century and was among the Vians who, in 2268, tested Gem to determine if her species was worthy to be saved from the impending nova of their star Minara. He possessed the ability to transport the entire population of Gem's species to a safe location.

He possessed the ability to read the minds of humanoids. Thann possessed handheld devices capable of inflictin torture, healing powers and transportation that were attuned to the thoughtwaves of the individual carrying them. He was all intelligence, no emotions and ruthless. He would sacrifice any number of humanoids to see if Gem was worthy to save.

He and his companion kidnapped James T. Kirk, Spock and McCoy in order to test Gem's compassion and self-sacrifice. They were tortured and McCoy was almost killed. When he was convinced that she had the qualitiy that would establish a quality civilization, he healed McCoy and saved her world. (TOS: "The Empath")

Thann was played by Willard Sage. The character name is from the script and onscreen credits and is not spoken in the episode.