Nicholas' reputation for generosity and kindness gave rise to legends of miracles he performed for the poor and unhappy. He was reputed to have given marriage dowries of gold to three girls whom poverty would otherwise have forced into lives of prostitution, and he restored to life three children who had been chopped up by a butcher and put in a brine tub. In the Middle Ages, devotion to Nicholas extended to all parts of Europe. He became the patron saint of Russia and Greece; of charitable fraternities and guilds; of children, sailors, unmarried girls, merchants, and pawnbrokers; and of such cities as Fribourg, Switz., and Moscow. Thousands of European churches were dedicated to him, one as early as the sixth century, built by the Roman emperor Justinian I, at Constantinople (now Istanbul). Nicholas' miracles were a favourite subject for medieval artists and liturgical plays, and his traditional feast day was the occasion for the ceremonies of the Boy Bishop, a widespread European custom in which a boy was elected bishop and reigned until Holy Innocents' Day (December 28).

After the Reformation, Nicholas' cult disappeared in all the Protestant countries of Europe except Holland, where his legend persisted as Sinterklaas (a Dutch variant of the name Saint Nicholas). Dutch colonists took this tradition with them to New Amsterdam (now New York City) in the American colonies in the 17th century. Sinterklaas was adopted by the country's English-speaking majority under the name Santa Claus, and his legend of a kindly old man was united with old Nordic folktales of a magician who punished naughty children and rewarded good children with presents.