Prince Arthas (A.K.A. The Lich King)- Warcraft 3/World of Warcraft.
He went on an insane purge of all the zombies from his land, killing any humans that had been infected or stood in his way. When he went to Northrend, the place the undead were coming from, his men wanted to go home. He hired mercenaries to burn the ships that took them there, trapping his men in a frozen wasteland, and then killed the mercenaries. He sought out the cursed blade, Frostmourne, and nearly killed his best friend. (He thought he was dead but he was just unconcious) He then went home, killed his father, the king, and plauged the lands with diseases and zombies. He then killed his former teacher and friend, Uther, because Uther tried to stop him from ressurecting a powerful necromancer. Then he went to the elven lands of Quel'thalas to use their magics to summon a portal that let the powerful demon lords onto the world.
Later, he went back to northrend, taking the frozen throne from Illidan and becoming the lich king. About 4 years later, he attacked the orcish capital of Orgrimmar and the human capital of Stormwind with zombies, killed two of their most important leaders, destroyed the native northrend civilations of the Vrykul, the Nerubians, the Fenzyheart, and the Oracles, then hijacked the Undercity from Lady Sylvanas, and commanded his zombie hordes to strike fear into the humans by killing civillians. He also ressurected an elite team of Death Knights, dead heroes of the world who had been zombiefied. Assualted light's hope chapel with unmeasurable forces, and crashed the Argent Tournament. He then was killed by a party of adventures and Tirion Fordring.