Zetarian
History:
Mysterious noncorporeal life-forms, the last survivors of the planet Zetar. The Zetarians wandered
through space for millennia, searching for a body in which they could live again. They thought they had found such a body when they
discovered Enterprise crew member Mira Romaine in 2269. When Romaine's fellow crew members discovered that her mind had been invaded
by the Zetarians and that she was in danger of losing her identity, Romaine was placed into a decompression chamber where the
Zetarians were driven from her body.
TOS "The Lights of Zetar" ; Star Trek Encyclopedia II
.