Arthas Menethil

Prince Arthas Menethil was the son of King Terenas Menethil II of Lordaeron and heir to the throne. He was trained as a Paladin by Uther the Lightbringer. Although he seemed like he would be a champion of the Light and a good king, he turned out to become one of the most evil beings on Azeroth, although not entirely by his own will. After having his soul taken from him by the cursed runeblade Frostmourne, he went on to become a Death Knight, and the greatest champion of the Scourge, destroying the kingdoms of Lordaeron, Quel'thalas and Dalaran.

He would eventually return to Northrend, where he would merge with the Lich King, Ner'zhul, and would overcome him, becoming the dominant personality of the Lich King. At the end of the Siege of Icecrown Citadel, he was slain by the Paladin Tirion Fordring, and Frostmourne was shattered. He died in the arms of his ghostly father, and let the mantle of the Lich King fall upon someone else's shoulders.