The Deadites are undead creatures that can come into our world through reading aloud incantations from the Necronomicon Ex-Mortis. The demons that are summoned through the incantations can possess a person, creature, or inanimate object. The things that become possessed go through physical changes and are given super-natural abilities. The demons can possess more than one host through biting. The only way to successfully kill a Deadite is by destroying the brain of the person possessed.
The deadites usually have continual run ins with Ash Williams. Occasionally, they will have to fight other heroes like Darkman, Cassie Hack, or other heroes that Ash might find himself allied with.