'Santa' as they prefer to be called is an individual that has had a push into madness. With the trauma of, the world ending, alongside previous traumas that occurred, it tends to do that to people. And all that matters is the fact that this individual has been pushed into this state of mind. 

Imagine it as say one of the Hunters, of the Cannibal Farms. They weren't all right in the head and the various events they suffered drove them to madness of devouring people alive. 

And records can easily get destroyed. With the world's power supply, and everything gone, it is hard to obtain files, and they make sure that no one can truly identify them with the past. As, well Santa doesn't care about who they were before this, all that matters is who they are now. 

Anyway, I can answer whatever questions you want to ask about the character.