Mordegon

Mordegon is the main antagonist of Dragon Quest XI. Prior to the beginning of the game, he possesses King Carnelian so that he can label him as the Darkspawn and have his knights hunt him down.

He first appears in person when the hero goes to Yggdrasil. He crashes the Yggdrasil Tree into Erdrea, resulting to countless deaths. Veronica sacrifices herself to ensure that the others survive.

He then has his minions (led by the Spectral Sentinels, which are themselves led by Jasper) search for survivors so that he can take their souls. He sets up operation at the Fortress Of Fear, which was where the Yggdrasil Tree was.

As a side-effect of Mordegon taking over the world, monsters such as the Gloomnivore are able to take advantage of the situation.

However, the hero eventually defeats him. Afterwards, the hero then goes back in time to prevent the destruction off

It is eventually revealed that he is in fact the evil side of the mage Morcant, who betrayed Erdwin in an attempt to claim Calasmos' power for himself. Though he still attempts to prevent Calasmos from being resurrected, he attempts to take over the world.