In Fallout 4, not only is Santa Claus real, he wears a damn Power Armour suit. Because of course he does.
Here's an amazing Christmas celebration by Tyrannicon within Fallout 4 -- he basically pretends to be Santa Claus, and goes around the Commonwealth saving the day with the help of candy cane mini guns. Also, actual candy canes. It's a hoot.
Thanks for the tip, James.