Burning Legion

The Burning Legion is a faction of demons, evil warlocks, tricksters and other evil entities. Their ultimate goal appears to be the destruction of as many worlds as possible.
The sky of the Outlands is littered with planets that they have destroyed and, arguably, "Draenor" itself counts among them. Azeroth, however, appears to be a sticking point.
They are responsible for the Scourge and the Sunwell disaster, among other things.