Santa Claus is a traditional, secular figure of Christmas good cheer who is the best known (at least in modern times) mascot of Christmas, developed in the United States as an amalgam of the story of St. Nicholas and various other seasonal folk heroes, with many aspects provided by the classic poem A Visit From St. Nicholas. The Santa Claus myth is based largely on the Dutch holiday of "Sinterklaas" (a hastily pronounced "St. Nicholas", who comes down the chimney on the 5th/6th of December) and the imagery of the Saint in question carried over to his North Pole incarnation. (Note that in several countries in Europe, Sinterklaas and Santa Claus are considered two entirely different characters, each with their own elaborate holiday.)
The modern figure of Santa Claus who we know is a fat bellied happy old man having a long white beard who wears a red coat with white collar and cuffs, white-cuffed red trousers, and black leather belt and boots and carries a bag full of gifts for children.
He lives at the North Pole in a large workshop staffed by elves which produces toys year round, and every Christmas Eve he sets out in a flying sleigh pulled by nine reindeer and delivers toys and other gifts to the children and children-at-heart of the world out of the improbably large sack he carries with him, entering their houses by the chimney, filling their stockings, putting larger gifts under the tree, partaking of whatever food and drink the family left out for him (traditionally cookies and milk), then leaving how he came in.
Santa Claus appears in many Christmas specials and movies. His portrayal in them varies in many ways