Telepathic, noncorporeal beings whose true form drives most humanoids insane; Zero in Prodigy is a Medusan.
The Medusans are a highly advanced, noncorporeal species of telepaths. Their thoughts are considered among the most beautiful in the galaxy, but their true appearance is so alien that a humanoid who sees one is driven mad, so they travel in protective containers.
In the original series episode Is There in Truth No Beauty?, the Enterprise carries the Medusan ambassador Kollos, along with Dr. Miranda Jones, a blind telepath who uses a sensor web to see. Larry Marvick, one of the designers of the Enterprise's engines, sees Kollos and goes insane, sending the ship far outside the galaxy. Spock mind-melds with Kollos to navigate it back but later sees the Medusan unshielded and loses his sanity until Jones helps him.
In Prodigy, Zero, the Protostar's engineer, is a Medusan who wears a containment suit to protect others from the sight of their energy form, and is a gentle telepath.