Here's the story. 6,000 years ago, an old, bearded, White dude who spoke perfect English, created everything. His bestest thing was a bunch of hairless pig-monkeys. Now, this old White dude, he knows everything. So, he knew that his pig-monkeys would piss him off.
So, he waited 4,000 more years, then he sent one of his invisible flying slaves to fuck a White teenager. She gave birth to a kid in a manger. That kid was his own father. But the old White dude knew he'd have to kill the kid so he could forgive the pig-monkeys for doing what he already knew they'd do. All that happened one morning when it snowed in the desert.
Then, in the 1940s, two companies formed America's first "synergy," and revived a Gothic legend about a pagan Germanic aristocrat, who gave children baked goods on the Winter Solstice. They fattened him up, gave him a ridiculous red suit, some flying ungulates, some pituitary dwarves, and a polysyllabic catch-phrase.
He would serve the purpose of coercing Americans into spending themselves into debt, every 25th of December. If you're Coke or Macy's that's some good work, right there.
In the year 2000, the manger-kid was supposed to come back from the dead - again - and destroy all the stuff he created 6000 years earlier. And he was gonna pick Jerusalem, Israel to do it in, because... because... well, because somebody said so... that's why. Well, somehow he screwed the pooch on that deal, so now we're waiting for him to get it together and finish destroying us.
Merry Christmas Y'all. I love each and every one of you. Keep reading hard.
St. Nicholas (Santa Claus in German) was a real guy. He was born to a wealthy aristocratic family but lived in a Christian monastery. He anonymously gave away his family inheritance to needy families. None of his philanthropy became public until after his death. As far as his modern image, you're right it was created on Madison Ave. The original Christmas celebration was very similar to the Saturnalia Holiday which concluded on Dec. 23rd (very rowdy), and of course the Mithras Holiday was on Dec. 25th.