Arawn

The Terrible Demon King, he slept for a thousand years after his body is critically injured on the battlefield. Drwc resurrected him using a ritual involving Riannon as a living sacrifice but is instead killed by Arawn after he saves Riannon from Drwc's control. When Arthur challenges Arawn while attempting to "save" Riannon from him, Riannon steps in by declaring him as their chieftain, taking them both by surprise.