Dark Elves, Drow.

One of the Many off shoots of the High Elves. They're name in elvish means the betrayers, however in their language it is more accurately translated to the betrayed. However the specifics of their original historic foundations is vary much left to debate, ten thousand years is a long time for any race no matter how long they live to get the specifics correct. What is known is that they fled the surface world and tunneled down into never before seen parts of the Underdark unclaimed by the Kingdoms of Drwarves.