Sauron

Sauron, once known as King Isildur the Wise, was once the King of Angmar, and was corrupted along with others by one of the nine Rings of Power given to the High Council of Angmar by the Lich King Ner'zhul over ten years before the events surrounding the Third War occurred. He and the eight other lords of Angmar received incredible power from the rings, which they used to further their own ambitions, but eventually the Rings completely corrupted them and turned them into the ghostly, undead Nazgûl, slaves to the will of Sauron. Sauron was responsible along with his second-in-commander Khamul for leading the Scourge to war during which the event was to be known as the "War of the Spider".