Might of Menethil

Might of Menethil is an epic two-handed mace. It was the highest damage-causing weapon in World of Warcraft before The Burning Crusade next to Andonisus, Reaper of Souls, with the latter being restricted to use only within Stratholme and only for ten minutes.

Source
This item was dropped by Kel'Thuzad in Naxxramas.