- "How compact your bodies are. And what a variety of senses you have. This thing you call language, though... Most remarkable. You depend on it for so very much, but is any one of you really its master? ...But most of all, the aloneness... You are so alone. You live out your lives in this shell of flesh... self-contained, separate... How lonely you are... How terribly lonely."
- ―Ambassador Kollos, a Medusan, experiencing being in a humanoid body while in a telepathic mind link with Spock
The Medusans are a sapient species of telepathic non-humanoids which are described as having the most beautiful thoughts known in the galaxy. Their physical appearance in sharp contrast is so hideous that even the quickest glance at them will cause madness and might even result in death by multiple organ failure in a Human observer. Vulcans are more resistant to the effects, being able to stare at a Medusan while wearing a special kind of visor. The Medusans are also regarded as excellent outer space navigators, partially a result of their natural sensory system being radically different from that of other races.
Despite the obvious obstacles to interspecies diplomacy, the benevolent and curious Medusans have shown interest in establishing diplomatic relations with the United Federation of Planets, with most of it being conducted between Medusan Ambassador Kollos and a blind Human telepath named Dr. Miranda Jones.