Shadowmaster

Shadowmaster A wizard on Thundera who used a cloak of darkness to conjure his magical powers and attempted to take over the planet. He was defeated by both Jaga and Lion-O's father, Claudus, and was then banished to the "Shadow Realm," but he managed to escape years later, kidnapping Claudus just before Thundera was destroyed. Through a sequence of nightmares, Lion-O eventually learns of his father's imprisonment in the Shadow Realm and is able to rescue him. The Shadowmaster has arguably come closer to defeating the ThunderCats than anyone else. In his one-time assault on the ThunderCats, the Shadowmaster would have succeeded had Mumm-Ra not interfered for fear that the Shadowmaster would replace him as the chief servant to the Ancient Spirits of Evil.