In Fables Santa Claus is one of Hope's Paladins, the "Hope for Justice" and the "Hope for Reward." He lives at the North Pole, each year he delivers presents to the good and coal to the bad.
Santa Claus appears sparingly across the story of the Fabletown citizens. He caught Jack trying to steal his list. Another time he conjured the dead wife of Flycatcher for one last kiss to turn him back into a man. The Wolf children also interact with Santa on a few occasions.
Finally, in his role as one of Hope's Paladins, he helped Rose Red decide which kind of hope she would champion.
Despite being one of Hope's paladins, he directly answers to Winter Wolf as its shown when she asks for his obedience in siding with her mother as he was also an aspect of Winter and thus also under her jurisdiction.
He pens down the list of naughty and nice children from all over the world and rewards them accordingly on Christmas Eve. Instead of traveling the world visiting one house at a time he has a version of Omnipresence in which he visits all the houses simultaneously in a single trip.
If someone happens to come across Santa during his delivery, they have the option to ask Santa a question with the cost of receiving no present from him that year, but getting an answer to their question instead.
- Bill Willingham stated in the Fables Encyclopedia that Santa is a very powerful Fable, almost god level, along the lines of Hope, Mister Dark, and the Four Winds. He's also one of those who loses too much magic if we see him too often, so he only appeared in Fables once in a great while.