Red is a Dark Spawn Lord and is the chief anatagonist of All Dogs Go To Heaven 2 - a powerful demon who was aided by Carface his plan was to use the magical Horn Of Gabriel to literally pull all the dogs from Heaven and imprison them in an island prison.
To this end, he tricked Charlie into aiding him via creating magical-collars and forcing him into a deal: this climaxed in the demon managing to actually get the horn and he began to imprison the inhabitants of Heaven and growing into a monster of seemingly apocalyptic proportions, causing the sea itself to start to rise around the island in a massive whirlpool.
However, Charlie and his friends decide to fight back, resulting in a battle that ended with Charlie blowing the horn: reversing the evil spell.
Red, who had already been weakened by the battle, was ultimately dragged back to Hell.
Role in the series
As it turns out, Red had been one of the original Dark Spawn lords under the command of Chernabog billions of years ago. He was also one of the few demons who remained loyal to the dark lord even after his imprisonment in Bald Mountain. Currently, he and his minion, Belladonna, have found a way to escape Hell, but have not yet appeared in the Spongebob adventures series to plague Spongebob's life. Red's relationship with Carface has, on the other hand, been ripped off into Fagin and Ratigan's relationship because Scroopfan thought of the idea that Ratigan ends up in a simuler situation with Carface, a nortorious criminal mastermind becomes a second banana to a demonic villian, would be interesting to see again. If Red does appear in the series, he will have to have his skeletal cat mnions be replaced with the puppy goblins from the first film because Scroopfan hates evil cats, and wants to see Red actually have different minions than instead of cats. Besides, the idea that dogs only go to heaven, and that cats only go to hell seems a bit racist to him. That's why Red was replaced with Fagin in the very first place.