Evil Ash, also known as Bad Ash or Deadite Ash, is the main antagonist of Army of Darkness. He is Ash Williams's dark side, and is also implied to be the evil force from the film's predecessors, which was sent back through the time rift moments before Ash was.
An unseen evil force, he chased Ash through the forest (similar to the first two films) as he was on his way to get the Necronomicon from the cemetery. He chased him into a windmill and entered the mirror. When Ash smashed the mirror, it took the form of several Tiny Ashes, which tortured him until one jumped down his throat, and the others ran off and disappeared. Manifesting into his dark side, the Tiny Ash separated from Ash, as his evil clone, Evil Ash. Ash shot him in the head with his shotgun and dismembered him with his chainsaw, and the buried him. His head survived long enough to taunt Ash more.
When Ash retrieved the Necronomicon, he was supposed to speak the words "Klaatu Verata Nikto", but forgot what the word "Nikto" was, and said it wrong, coughing so it sounded like he said it. This raised an army of the dead, and Evil Ash was reawakened as a Deadite. The leader of the Deadite army, he kidnapped Sheila and led the Deadite army to get the Necronomicon. Initially reluctant, Ash decided to lead Arthur's army into battle against the Deadite army. Ash fought Evil Ash and set him on fire, turning him into a skeleton. He attacked Ash one more time, but when he unwittingly jumped onto a catapult with a bag of gunpowder whose fuse was ignited by Ash's torch, Ash activated the catapult to send Evil Ash flying into the air with the bag of gunpowder, which exploded and completely destroyed him.
Without their leader, the remaining Deadites were forced to retreat.