After sucessfully escaping The Scourge in the Plaguelands, two foiled assasination attempts, and defeating Illidan and his Naga, King Arthas finally reaches the Frozen Throne in Northrend.
I spite of all the voices in head, he obeys the Lich King's voice and fulfills his mission by freeing the spirit and armor from its icy prison; only to be posessed by it and thus becoming the new Lich King incarnate until this very day.
Arthas, once a noble paladin of Light, plunges further into darkness...