What backstory would you give to this guy

reincarnation of a toilet

Walked into the wrong branch of Apple Co.

He got his garlic bread stolen so now he kills people

He's a professional photographer

A normal human being, terribly disfigured by maniacal scientists to the point he is a poop emoji, who has no other purpouse in life to get REVENGE.

A guy playing a video game thought the avatr was funny and so he used it