A visitor from another galaxy who uses illusions of a haunted castle to study the Enterprise landing party, and who ultimately tries to help Kirk.
Korob is one of two explorers from another galaxy who arrive on Pyris VII in Catspaw. In humanoid form he presents himself as a sorcerer in a gloomy castle, using a device called a transmuter to create illusions drawn from humanity's oldest fears of witches and the dark.
Korob and his companion Sylvia hold Kirk's landing party captive and control Scott and Sulu. Unlike Sylvia, who becomes entranced by human sensations, Korob begins to doubt their mission and tries to free the captives, and is killed for it. He was played by Theodore Marcuse.