@NoodlesWell actually Christmas is a christian holiday to start with. It celebrates the birth of Jesus, who was apparently born December 25th. I never cared much for Christmas besides an excuse to eat some food and catch up with some family.
Santa Claus came later. Pretty sure he was introduced by Coke Cola or something. Anyway Santa Claus was based off Saint Nicholas, basically a guy who helped out some prostitutes. Not too sure how he ties in with the whole mess, but he does
Not entirely sure on the origin's other than bits and pieces, but it is always fascinating learning the origins of such mainstream holidays in the western world.
Such as Easter or Halloween. Both started off as religious festivities (At least I think Halloween was religious >.>). The origins of both are fairly interesting reads. As is most festivals and holidays.