Gaheris.
Gavin's younger brother.
One of the Knights of the Round Table who fought and died together with Gareth while trying to stop Mordred.
Now they have returned, pouring out of the Underworld successively, trying to drag their enemy into the Abyss of No Bottom, which made perfect sense, and he should just standstill and let them kill him.
Lancelot stared at Gaheris:
"Who brought you back?"
Gaheris sneered:
"Someone we both know introduced me to it. He is now called the Messenger of Ash, he submits to a powerful god. Although I despise his actions, since he gave me a chance to take revenge, I've come back.
"Obviously I'm not the first, and if you win this time, it doesn't mean you can get rid of us. I, Gareth, and all those you killed, no matter how many times we fall back into the Underworld, we will keep coming back.