The origins of Christmas are pretty much well known. There was a whole virgin birth in a manger while trekking across Africa or something, but what is less well known is that it was originally a pagan holiday which was criminalised until 1907 in the US.
It was in 601 that Pope Gregory I wrote to Melitus (his missionary in England) telling him "not to stop such ancient Pagan festivities" but to "adapt them to the rites of the Church, only changing the reason of them from a heathen to a Christian impulse". So all those who have been claiming for years that Christmas was, in fact, actually a pagan holiday - you were right and Pope Gregory I handily put it in writing for you.
That said, Christmas also moved around the globe between 900 - 1000 Common Era (C.E.) and was adapted to match their winter celebrations there as well. Christmas evolved slowly and gradually, with no firm mention of it until the mid 11th century, where we actually find the first reference to it. It evolved and changed and grew to become what we now recognise with egg nog and a tree, but it was not without its detractors.
In England, parliament banned Christmas for 12 years from 1647 under Cromwell. That ban was lifted only for it to be imposed in the Massachusetts Bay Colony in 1660. This ban on Christmas, becoming law in many places, lasted until the apparently progressive state of Alabama was the first US state to legalise Christmas in 1836, meaning there was almost 200 years during which it was criminal to celebrate Christmas in the US. Oklahoma became the very last state to make Christmas legal again in 1907 despite the US making it a federal holiday in 1870.
So while you may have known that Christmas was originally pagan festival, you might not have known that in the UK it was made illegal for 12 years and in the US it was illegal for 260 years. Want to know more? Check out this really amazing infographic all about Christmas here: The History of Christmas