Gaelion, The Dragon Emperor

Originally "The Weakest of The Dragon Emperors", Gaelion was inadvertently killed by Sword Hero Ren Amaki as part of a "Quest"; who leaves behind the corpse following game logic that it'd despawn. The resulting corpse poisons the land and Gaelions' hatred of the Sword Hero for killing him and indirectly selling Gaelions' adoptive daughter into slavery reanimates his corpse.

Example of:
Dracolich