The Wyrm on which Chaos rests, the source of the Eye of the Serpent (now the Jewel of Judgement). The opposite of the Unicorn, possibly because of the whole losing an eye thing, possibly not. Pretty darn powerful, and pretty darn entropic. Not terribly active.

When things die in the local universe, they go into his scales. (Amberites go into the Jewel.)

The Serpent’s manifestation in the sky of Chaos was considered a sign of an impending apocalypse. If the Serpent had not returned to his place under Chaos, it would have settled into the Sea of Chance and been destroyed.

The Serpent was injured by members of the Black Council, and shifted position causing the Shadow Purge.