Medusan

Medusans are a one-episode energy cloud race from the TOS episode "Is There in Truth No Beauty?"

"While the thoughts of the Medusans are the most sublime in the galaxy, their physical appearance is exactly the opposite. They have evolved into a race of beings who are formless, so utterly hideous that the sight of a Medusan brings total madness to any human who sees one."

-- Captain's Log

Alien of the Week Features

• The Medusan form is incomprehensible to humanoids: a person who sees a Medusan will go insane and soon die. Vulcans can tolerate the appearance of Medusans if they look through a special filter, but without the filter, they too will go mad and die from the sight. When interacting with humanoids, Medusans occupy opaque travel pods with sensors and communications gear to protect their associates.
• Medusans are highly intelligent.
• Medusans are telepathic, but such contact is limited to communication with other telepaths.
• Medusans have an innate sense of the location in time and space that makes them intuitive navigators.