Legendary for his generosity to the poor and protector of the innocent and wronged, St. Nicholas was Bishop of Myra (now part of modern Turkey) and is particularly venerated in Russia. There are many stories about him and he is the historical figure who has become Santa Claus.
To save three daughters of a poor man from being sold into slavery, he dropped bags of gold for dowry payments down their chimney. These three purses of gold became symbolized by three golden balls making St. Nicholas the patron of pawnbrokers.
He is supposed to have brought three children back to life who had been murdered and hidden in a barrel of brine.
He is also said to have persuaded some thieves to return their plunder leading to his becoming the Patron against robbery, this led to the expression for thieves 'Saint Nicholas' clerks' as well as the expression to 'nick' something.
He is the patron saint of many things and is one of the most popular saints in both the Eastern and Western church, being depicted by more artists and icon writers than any other saint with the exception of the Blessed Virgin. There are many sources of information on St. Nicholas including Lives of the Saints, The Catholic Encyclopedia, Saints Index on Catholic Forum and an excellent website devoted to him, from The Saint Nicholas Center