Icecrown

Kel'Thuzad is the single cutest success story in fiction, though?

As a living human, he was a sad Kirin Tor member of the Council of Six, the Kirin Tor’s high council. Despite his success as a mage, he was lonely and sad, no one liked him, and he deeply resented this, as he never really could get close to anyone. One day, Kel'Thuzad said “ENOUGH”, sold EVERYTHING he had (and he had a lot of stuff, remember, he was one of the six leaders of the Kirin Tor, the dude was rich beyond our wildest dreams), hid the money, and then went ALONE to the most dangerous part of the world, Northrend, where none dared to tread.

When he arrived there, following the whispers of the Lich King inside of his head, which was more meaningful bonding than any he had back on civilization, the undead guards didn’t even attack him, as he was expected and a guest of the Lich King. So he went to Icecrown, cracked open a cold one, and had a beer with Big N. While they were talking about the baseball game, Kelly asked the Big Man “hey dude so you cool if I serve you?” and Nernie was like “yeh” and BAM he removed his soul and BAM he replaced it with happiness. Not really, but that’s kinda what happened. So Ner’zhul told him “ok man go make a religion that worships me” and Kel was like “cool” so he did and he started a BIG CULT and he finally had friends!

Then Arthas came and said Hey Don’t Do That, but Kel just said “You and I… Are gonna be BEST FRIENDS” and then Arthas cracked his skull open with his big hammer and killed him, but then some months pass and Arthas, now Bad Arthas, desecrates an entire Elf city to perform a ritual that revives Kel’Thuzad as a LICH and they HIGH FIVE and Arthas says “GOLLY GEE YOU WERE RIGHT”.

And since then, they just kicked ass together and performed a shitload of evil rituals and almost straight up ended the world, and since then, Kel'Thuzad has only been happy, and like the ONE person that Arthas has been very courteous and friendly with, even calling him his most trusted friend when they part ways in The Frozen Throne. Which is very telling since Arthas is the kind of guy that tortures elf girls for funsies and that’s why we have Sylvanas “Fuckhouse” Windrunner shooting sharp arrows and sharper glares around assorted graveyards.

TL;DR: Kel'Thuzad was a SAD, RICH, SUCCESSFUL, LONELY living man, and in accursed undeath, he became HAPPY, POWERFUL, and made MANY FRIENDS. He also owns a CAT named Mr. Bigglesworth.