He is an incredibly powerful undead being who wishes to destroy the earth. He is the leader of Blood Spiral Clan.
Betrayer serves as the minor character until the end of the series where he finaly appears and nearly succeeds in his plans. He was sealed within the spiral mark by lord Casterwill and when that is revealed it is shown that The Betrayer is ancient and was the arch-enemy of the Casterwill family.
The blood spiral clan worships him as their god, and would follow any of his orders, some of the members where brainwashed by him.
He also has the legendary titan of betrayal. He is nearly immortal and can do almost anything he wants.
Even throught he is nearly immortal he still can die, in the end The huntik foundation locates his weak spot and destroys him once and for all. The source of his power, Red comet still existed and its possible that his being is still alive.
He speaks without his mouth moving and always attacks his enemies from behind.