Parmen was a Platonian male, born circa 34 BC, who served as leader of the Platonians. Like other Platonians, Parmen possessed psyhokinetic powers and used them to amuse himself by torturing others, and making them do his bidding.
Parmen was close to death in 2268, after a leg wound had become infected. Philana, Parmen's wife, became concerned and contacted the USS Enterprise to ask for urgent medical treatment for her husband. The Enterprise responded and Dr. Leonard McCoy was able to heal Parmen's wounds. Unfortunately, Parmen realized that the Platonians needed a doctor and tried for force McCoy to remain behind. When McCoy refused, Parmen tortured the rest of the landing party, forcing them all to remain.
Thankfully, McCoy was able to determine that the Platonians received their great mental powers from a substance in their food, known as kironide. McCoy then injected the Enterprise crew with kironide, and they to began to exhibit great mental powers, which helped them defend themselves from Parmen and his people. (TOS episode: "Plato's Stepchildren")