Quote Originally Posted by Con_Carne View Post
Anything?
Anything, as long as you understand that this will only be your personal "head-canon", that is, your personal story for your character. Whether or not you can get other people to play along is what role-playing is all about.

That said, it's generally a good rule-of-thumb to stick within established lore as far as possible. So, extraordinary origin stories — such as being from another dimension or world — would require extraordinary explanation. Eventually, if it gets too far-fetched, you'll find in harder and harder to keep your character's story grounded and believable.