I draw fnaf (in general)

maybe I'm missing details from the books that prove me wrong with this (I haven't read the books in a long time), but then I remember that my whole thing is not following canon so...

He's just a representation of Fredbear, just an entity created by the agony of those who died in (and by) the Fredbear suit (which was a lot). He stole some kid's appearence to pretend to be human for this and that reason

So after he lost Andrew (him ending up in the stitchwraith) he just went wild while trying to find him (or anyone else really), the the stuff from TNK happened and Devon just kind of haunts him

So Kelsey's whole personality is based of bits and fragments of the souls that created him (mostly kids) and what Fredbear was thought to be, so he was mostly friendly. Then Devon joined and...well, Devon really wasn't known for being friendly?

so basically Fredbear/Golden(suit) = Kelsey = just an entity, not actually human