How Satan stole Christmas

So, St. Boniface is the asshole who started that.
http://www.bbc.co.uk/devon/content/articles/2005/12/05/st_boniface_christmas_tree_feature.shtml

It was on this trip, around the time of Winter Solstice, that he was said to have come across a group of pagans worshipping an old oak tree.

Horrified by what he saw as blasphemy, the all-action St Boniface grabbed the nearest axe and hacked down the tree. As he did this he called to the pagans to see the power of his God over theirs.

Pagan feelings were understandably mixed, but Boniface's actions were obviously taken in good spirit, with some of the tales saying he converted the pagans on the spot.

This is where the tale now divides. Some say St Boniface planted a fir tree there, but the most common idea is that a fir tree grew spontaneously in the oak's place.

The fir was seen as an image of God and many believed its evergreen symbolised the everlasting love of the Maker.

According to the myth, the next year all the pagans in the area had been converted to Christianity and hung decorations from the tree to celebrate what they now called Christmas rather than Winter Solstice.