- Q (in Star Trek, played by John de Lancie) is an immortal entity from a race of beings also known as the Q.
Q has appeared to the crews of several Starfleet vessels and outposts during the 2360s and 2370s. He almost always appears in the uniform of a Starfleet captain.
Q on MemoryAlpha (StarTrek Wiki)
There a LOT of other meanings for Q:
Related: Quakenet