It all started with Nicholas, a Greek bishop in what is now Turkey. He became the patron saint of children; his feast day on December 6th or 19th, depending on whether one follows the Orthodox or modern calendar. St. Nicholas/Father Christmas was transformed into Sante Claus in the U.S. by the early 1820s by writers like Washington Irving, who celebrated the Knickerbocker heritage of the Dutch colony of New Amsterdam. “Sante Claus” comes from the Flemish name for St. Nicholas, Sinterklaas.
The “jolly old elf” really got his persona going in the 1823 poem, “A Visit From St. Nicholas,” better known as “The Night Before Christmas.” This still-popular poem was published anonymously and is usually attributed to Clement Clark Moore. Moore was an Episcopal theologian and professor of Greek and Latin with a side-gig developing Manhattan’s Chelsea neighborhood. He represented the wealthy New Yorkers who turned American Christmas into a family and children-centered holiday instead of the sometimes rowdy open-air (and inside-tavern) communal celebration it had been.