Naraku

The Anime Empire
Having been persuaded with much more power by Shinnok to help get the Shikan jewels if he fights for him, Naraku deserted Emperor X's empire becoming a traitor to the group. With his great abilities of manipulating people, Shinnok has a rather excellent strategic schemer to help turn enemy factions against each other and even heroes if he senses any negative emotions coming from them.

LOTM: The Angels Return
When Sesshomaru brought down the Angels and their friends, it was revealed that he had done it because Naraku was holding captive someone Sesshomaru cared about: a human girl named Rin whom he had rescued.

Being the monster he was, Naraku instead took the rest of the Shikon Jewel Shards, fused them to what he had of the jewel, and declared that he would fight everyone when they were well and Rin would be returned...if they could find him. Enraged at this, Sesshomaru vowed to give Naraku a worthy opponent...and told him to be careful what he wished for!