Sauron

Sauron is the big bad of the Lord of the Rings franchise and the reason behind much of the changes and upheaval that the LoR world has faced during it's current ages. He is one of the first proper Dark Lords in popular fiction; while Voldemort, Doctor Doom and Abaddon were in kindergarden like some evil version of the muppet babies learning what the word 'bad' meant, Sauron was out cracking heads and getting shit done.

A hilarious note is the fact he wasn't even the big bad to begin with; he was seduced into his new lifestyle by an even bigger dick who Sauron was the chief underling to. Once his boss was beaten up by the other Ainur (Tolkien's versions of archangels in this universe), Sauron fled across the sea to middle-earth, where he used his great cunning and sorcery to work events to his favour.

Like any evil villian, Sauron was then beaten time and time again but he always managed to flee while screaming "I'll be back" over his shoulder. Finally having enough for the subtle methods, he tried to merely maul everyone to death in his big destroyer form with an army of orcs but thanks to some pesky men and elves, he got his finger with his magic ring (which contained a great deal of his power and life) cut off and as a result became a highly pissed off spirit that kept trying to come back, knowing that if he could get his bling back again he could have another bash at taking over the world.