Cujo

Cujo is a dog. To be specific, BestNightGuard's dog. He runs, he wags, he licks, he eats, he sleeps, and pees. What else would a dog do? Oh, and he's immortal.

But to be really HECKIN' specific, he wasn't always BestNightGuard's doggo. He used to belong to a king named Stephen. Now he doesn't. The end.