the Lich King

Kil'jaeden the Deceiver created the original Lich King from the spirit of the orc shaman Ner'zhul for the purpose of raising an undead army to weaken Azeroth in preparation for the Burning Legion's invasion. Initially trapped within the Frozen Throne with Frostmourne, the Lich King eventually betrayed Kil'jaeden and merged with the human Arthas Menethil. At the climax of the war for Northrend, Arthas the Lich King was defeated by Highlord Tirion Fordring and his champions. After the destruction of Frostmourne and the death of Arthas, Bolvar Fordragon became the new Lich King in order to keep the undead Scourge in check. Bolvar was later defeated by Sylvanas Windrunner, who also destroyed the Helm of Domination, making the position of Lich King come to an end.