Q CONTINUUM

The Q are a non-corporeal hyper-intelligent and nearly omnipotent beings with the ability to warp reality at a whim, ranging from appearing in any place they choose to rearranging the cosmos themselves. They are invulnerable and immortal except when faced with weapons designed by others of their kind: in sufficient numbers, Q can strip other Q of their powers and make them mortal. They claim to be largely indifferent to the affairs of the non-Q beings living in normal space, or in the many dimensions parallel to their own, considering them to be insignificant and childlike, though sometimes amusing as only children can be. However, they are clearly very interested in some species, humans among them, subjecting the human race to various tests. These tests often imply that they feel somewhat threatened by a species's potential, but are intrigued by it as well. The Q are apparently all individually named Q and are usually in an extra-dimensionnal plane of existence known as the Q Continuum that is not subject to linear time as normal space is. It has been suggested that the Q evolved since the Big Bang to their current state, and that possibly they were mortel physical beings very early on and that when they gave up their physicality and achieved their godlike powers, they also gave up any chance of growth or evolution since change was unnecessary. They usually appear to others as members of their species.
Note: The Q bears a lot of similitudes with Doctor Who's Eternals.
Source: Star Trek universe, Star Trek: The Next Generation, Star Trek: Deep Space Nine, and Star Trek: Voyager.