Norman
Norman's circuitry (remastered)
Norman was the "leader" of a group of androids who inhabited the planet Mudd.
In 2268, Harry Mudd, who became stranded on the planet which he named after himself, sent Norman to capture a Federation starship so that he could leave the planet in exchange for the vessel's crew.
Norman left the planet and, posing as a Starfleet sciences division lieutenant, signed aboard the USS Enterprise. After successfully taking over the ship, he redirected it to Mudd to carry out "Lord" Mudd's plan.
The plot ultimately failed. Captain Kirk and Spock correctly hypothesized that the android population was essentially a hive mind and that Norman was the central control locus. The androids were deactivated when Norman's processors were unable to deal with a flood of illogic presented to him by the Enterprise's crew.
The breakdown, however, was only temporary, as Norman returned to bid farewell to the Enterprise crew. (TOS: "I, Mudd")