Well Santa is a variant of a European folk tale based on the historical christian figure Saint Nicholas and the not so christian God Odin.
and it wasn't celebrated on christmas but on december 5/6th.
the date of celebration was changed to christmas by a company called Coca Cola to increase revenue from sales because so many people were already celebrating that day.
I can understand that some Christians might be pissed that one of there holy days was used like this but i don't really care.......because I'm not Christian
more on santa