Saint Nicholas (Agios Nikolaos, "victory of the people") is the common name for Nicholas of Myra, a Christian saint and Bishop of Myra in Lycia of Anatolia (modern-day Antalya province, Turkey, though at the time it was a Greek-speaking Roman Province). Because of the many miracles attributed to his intercessions, he is also known as Saint Nicholas the Wonderworker. He had a reputation for secret gift-giving, such as putting coins in the shoes of those who left them out for him, and is now commonly identified with Santa Claus. Nicholas was never officially canonised; his reputation simply evolved among the faithful, as was the custom in his time. In 1087, his relics were furtively translated to Bari in southern Italy. For this reason, he is also known as Saint Nicholas of Bari.

The historical Saint Nicholas is remembered and revered among Catholic and Orthodox Christians. He is also honoured by various Anglican and Lutheran churches. Saint Nicholas is the patron saint of sailors, merchants, archers, children, and students in Greece, Belgium, Romania, Bulgaria, Georgia, Russia, the Republic of Macedonia, Slovakia, Serbia and Montenegro. He is also the patron saint of Barranquilla (Colombia), Bari (Italy), Amsterdam (Netherlands), Beit Jala in the West Bank of Palestine, Liverpool (England) and Russia. In 1809, the New-York Historical Society convened and retroactively named Sancte Claus the patron saint of Nieuw Amsterdam, the Dutch name for New York City. He was also a patron of the Varangian Guard of the Eastern Roman Emperors, who protected his relics in Bari. So beloved is St. Nicholas by Russians, one commonly heard saying is "if God dies, at least we'll still have St. Nicholas."

Saint Nicholas Day is a festival for children in much of Europe related to surviving legends of the saint, and particularly his reputation as a bringer of gifts. The American Santa Claus, as well as the Anglo-Canadian and British Father Christmas, derive from these legends. "Santa Claus" is itself derived from the Dutch Sinterklaas.

The history of the festive Saint Nicholas celebration is complex and reflects conflicts between Protestantism and Catholicism. Since Nicholas was a canonised saint, Martin Luther replaced the festival that had become associated with the Papacy with a Christkind ("Christ child") celebration on Christmas Eve. The Nicholas celebrations still remain a part of tradition among many Protestants, albeit on a much smaller scale than Christmas. The Protestant Netherlands, however, retain a much larger Saint Nicholas tradition. Many Dutch Catholics, on the other hand, have adopted Luther's Christkind.