Why is St. Nicholas so important on Advent and Christmas?

Saint Nicholas of Myra has no connection with Christmas other than his feast day of December 6 falls in Advent. He is noted for his generosity to the needy, usually making his donations in secret. He is celebrated, primarily in Europe, on his feast day and Christmas is a distinctly separate holiday. Commercial interest hijacked Saint Nicholas a number of years ago and turned him into Santa Claus to improve sales during the Christmas season.