Kel'Thuzad: Right hand of the Lich king, tactical spreader of the scourge, headmaster of the Cult of the Damned, Master of Naxxramas and a powerful foe.
Quote about Kel'Thuzad by Commander Eligor Dawnbringer: "The lich, Kel'Thuzad. He serves the Lich King without question, a necromancer of great prowess in life, turned into a master of necromancy after his death. It is said he is the most loyal of the Lich King's subjects. Kel'Thuzad has survived trials that would have long since shattered the souls of even the greatest of the Brotherhood. He readily gave his life at Arthas' hand, later to be brought back - reborn in the power of the Sunwell. In the Plaguelands, Kel'Thuzad was again defeated by the agents of the Argent Dawn."
But in the hands of my "Casual raiding guild", Kel'Thuzad fell like a rock just one week after we entered Naxxramas the first time. I believe it all was a little too easy.