The Q

From Star Trek: Theurgy Wiki

One species that the Federation Security Council had marked as a threat was the collective species known as the Q. They were an omnipotent species of beings, residing in an alternate dimension they call the ‘Q continuum.’ Most of Starfleet's interaction with the Q has been through one individual of their species, who took a strange and special interest in Captains Jean-Luc Picard, Kathryn Janeway and Benjamin Sisko. Starfleet Intelligence hoped he remained the only curious member of the species, as even that one individual exhibited so many powerful abilities that the Federation would simply be unable to compete.