Garth of Izar from the episode “Whom God’s Destroy” in the original series
“It is a rare breed of individual who becomes a starship captain - possessing not only the required knowledge, instince and experience, but a certain vision and fortitude of spirit that sets them apart from all others. Thus, it is all the more tragic when such a person falls from grace, especialls in the case of Garth of Izar, a legendary captain who sinks into the depths of insanity. Captain Kirk encounters his longtime hero when he delivers revolutionary new medicine to Elba II, where the Federation maintains an asylum for the few criminally insane of the galaxy. Garth, now an inmate at the asylum, captures Kirk and Mr. Spock and puts a plan into motion to gain control of the U.S.S. Enterprise and beomre master of the universe.”
“Garth was the finest student at Starfleet Academy, and the model for all other captains in Starfleet. Garth sustained horrible injuries in an accident, and was treated on Antos IV, where he learned a technique of cellular metamorphosis that allows him to assume any shape at will. The accident left Garth mentally unhinged, and he tried to kill the entire Antosian race. Fath’s crew mutinied at this order, and the Captain was confined on Elba II. He intends to pose as Kirk and use the Enterprise to hunt down and destroy his mutinous former crew. He even believes he can use the small handful of other inmates to amass an entire fleet of ship and gain limitless power and wealth.
Demanding to be reffered to as Lord Garth, wearing a tattered fur robe and several medallions and pins, Garth’s demeanor can change from calm civility to murderous rage in an instant. Garth tortures Kirk to discover the code phrase that will allow him access to the Enterprise, and impersonates Spock when that fails. He even murders his insane Orion consort Marta as ‘entertainment.’
Garth stages a crude coronation of himself as master of the universe, and makes Kirk his crown prince and heir apparent. As Spock attempts a rescue, Garth changes his form into Kirk, but Spock sees through the disguise and stuns Garth. Afterthe other inmates are subdued, Garth is given the treatment he needs and begin his recovery, but without any memory of meeting Kirk.”