The Guardian prepares Sam for his destiny.
Sam looks a bit different before he goes batshit, doesn't he? he looks almost. normal. It's actually a little freakier than when he's screaming on the rooftop of the local McDonalds about cereal or whatever
I could've done the background better but oh well :I
Animal guardians/protectors/spirits are found in TONS of media and even mythology. It's a fairly simple idea to come up with. I basically came up with the Guardian on my own as Sam needed a way to receive his supernatural abilities, and thought a spirit that guides him would be a relatively easy and interesting way to achieve that
and it's a wolf because wolves are cool :I