Saint Nicholas (270-310) was at one time bishop of Myra (modern-day Turkey). He is supposed to have died on December 6 which is why his feast is celebrated on that date (in reality the party is the evening before). He went into the legends for his great generosity, therefore he is the patron of little children and school children.
The feast and celebrations of Saint Nicholas was abolished in some European countries after the Protestant reformation of the 16th century. The Dutch and Flemish however, have preserved this Catholic custom, and small children still await the visit of Sinterklaas (Saint Nicholas) on his white horse accompanied with Zwarte Pieten (black moors in colourful clothes) on the night of December 5.
Adults celebrate this feast too by wrapping a present in something creative (euphemistically: amateur handcraft) that's related to the other's life. Best thing about those silly presents however, is the accompanying poem which should be on rhyme and contain funny as well as sarcastical/cynical personal notes.

And the story goes on...
At the beginning of the 17th century, the Dutch emigrated to the United States, among other places, and founded the colony of New Amsterdam which became New York, iirc 1664. Over several decades, the Dutch custom of celebrating the feast of Saint Nicholas spread to the United States. Sinterklaas quickly became Santa Claus for Americans.

This philanthropist, an old man with a white beard and a long caped red coat/gown, remained, nonetheless, a moralistic figure. He rewarded deserving children and punished the difficult and unruly ones with the roe (= bunch of wooden twigs) and threads to take them back to Spain (I wish the latter were true).

After several decades, Christian society found it more appropriate to bring this children’s festival closer to that of Jesus. Saint Nicholas therefore made his rounds of Christian families during the night of December 24.