The 3 dark rulers of the Minecraft Universe Wither, Abyss Dragon, and Herobrine.

Wither controls the Nether. The dead are his servants and he laughs at even the heat of the sun. He was so dangerous and deadly that Notch destroyed him, but being the strong dark Necromancer he is he made a way fro him to be resurrected, Mixing his very soul into sand and his body onto his favorite servant, the skeletons. Now he waits for that one foolish traveler that is curious or expects something for his release.

He is sadistic, enjoying causing pain, and the only "Help" he ever gives anyone is his star, the center of his power, but he never explains how to use it.

Abyss Dragon rules over the land of Ender, known to miners as the End. His world is known as a glitch, easily earning that reputation for Miners never seeing anything but static in the air. His land is actually huge, a paradise for glitches, things removed, in a dimension not even Notch can see into, Those able to see and learn from the world end up becoming known as Modders and can greatly change the Overworld to their liking.

Abyss has little pleasure in killing, but he feels he must attack anything "whole" He protects his land and does not stop. He does not feel, he does not care. He is forbidden from leaing his world as he and the Overworld and Nether exist in different plains of reality. Anything he touches in the Overworld or Nether gets destroyed, even the ground he stands on forcing him to continue flying. Upon getting defeated he rapidly deteriorates, his body becoming unstable, but after he is gone he instantly respawns in the form of an Egg. Only one person knows how to hatch the egg, the person that created the world Notch couldn't enter......

Herobrine. A the unofficial dark ruler of the Overworld. He is also extreamly dangerous, so dangerous Notch had tried forcably removing him multiple times only for him to appear again angryer and badder than ever. He was the original "Player" who became a glitch after Notch messed up and created another glitch, the Creeper. Instead of Respawning like normal Herobrine was corrupted. His eyes are blind, but he can see every single block in the overworld as if the blocks themselves became his eyes. He didn't take the name Herobrine until He was replaced by another "Player" one that harassed the Villagers Herobrine took care of and destroyed the land worse than Creepers ever could. The PLayer called himself a Hero, and out of anger Herobrine became the salt of "Heros" Like salt to a field, finding them, and making sure they never come back.