Catholic Online (see excerpt below)
Greek Orthodox Archdiocese of America
Antiochian Orthodox Christian Archdiocese of North America
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It is the image of St. Nicholas more often than that of any other that is found on Byzantine seals; in the later middle ages nearly four hundred churches were dedicated in his honor in England alone; and he is said to have been represented by Christian artists more frequently than any saint except our Lady. St. Nicholas is venerated as the patron saint of several classes of people, especially, in the East, of sailors and in the West of children. The first of these patronage is probably due to the legend that during his life time, he appeared to storm tossed mariners who invoked his aid off the coast of Lycia and brought them safely to port. Sailors in the Aegean and Ionian seas, following a common Eastern custom, had their "star of St. Nicholas" and wished one another a good voyage in the phrase "May St. Nicholas hold the tiller". The legend of the "three children" gave rise to his patronage of children and various observances, ecclesiastical and secular, connected there with; such were the boy bishop and especially in Germany, Switzerland and the Netherlands, the giving of presents in his name at Christmas time. This custom in England is not a survival from Catholic times. It was popularized in America by the Dutch Protestants of New Amsterdam who had converted the popish saint into a Nordic magician (Santa Claus = Sint Klaes = Saint Nicholas) and was apparently introduced into this country by Bret Harte. It is not the only "good old English custom" which, however good, is not "old English", at any rate in its present form. The deliverance of the three imperial officers naturally caused St. Nicholas to be invoked by and on behalf of prisoners and captives, and many miracles of his intervention are recorded in the middle ages.
Curiously enough the greatest popularity of St. Nicholas is found neither in the eastern Mediterranean nor north-western Europe, great as that was, but in Russia. With St. Andred the Apostle he is patron of the nation, and the Russian Orthodox Church even observes the feast of his translation; so many Russian pilgrims came to Bari before the revolution that their government supported a church, hospital and hospice there. He is a patron saint also of Greece, Apulia, Sicily and Loraine, and of many citiesand dioceses (including Galway) and churches innumerable. At Rome the basilica of St. Nicholas in the Jail of Tully (in Carcere) was founded between the end of the sixth and the beginning of the seventh centuries. He is named in the preparation of the Byzantine Mass.