Medusans are a noncorporeal species renowned for their aptitude in spatial navigation and rendered virtual recluses by their unfortunate visage, which shocks humanoids into insanity on sight.
Traveling within his own transport chamber for safety as part of a Federation exchange project, Medusan ambassador Kollos checked aboard the USS Enterprise with a human engineer (Larry Marvig) and telepath Miranda Jones. Miranda had no fear of injury since she was blind, though she did not advertise that fact. Marvig was smitten with Jones, but when spurned he approached Kollos in a jealous rage, sending the starship out of the galaxy in his resulting madness.
Lieutenant Spock successfully mind melded with Kollos so that he could navigate the ship back and bypass the effects of the galactic barrier's sensory effects on humanoids thanks to Kollos' navigation abilities. He forgot to wear a protective visor when breaking the meld, and Captain Kirk realized too late to save him. Only Jones' could restore his sanity.