From Google:
Like many ancient traditions, the history of St. Nick's is debated. Some say St. Nick's Day is a decidedly German observance. Others say it is Spanish or Dutch. What is known is that St. Nicholas lived in the fourth century. He was a Christian prelate and the patron saint of Russia. Nicholas was a native of Patara, in the ancient district of Lycia in Asia Minor (now Turkey). He became archbishop of the metropolitan church in Myra, Lycia.
How he came to be so famous is a little bit of a saucy tale, not suitable for tender ears. Legend has it that he took pity on a poor man who was about to abandon his daughters to - get the kids away from the newspaper - prostitution. The story goes that he left trinkets for the man in his chimney. From this came the custom of secret gifts on the eve of the feast day celebrating St. Nicholas. Because of the close proximity of dates, Christmas and St. Nicholas Day are now celebrated simultaneously in many countries.