St. Patrick is the patron saint of Ireland. The interesting thing about that is he wasn't even Irish. He was actually captured by the Irish and taken as a slave from his home in Britain. He worked and lived in Ireland for about 6 years before he escaped and went back to his family.
After entering the church, he returned to Ireland as an ordained Bishop and worked in Ireland. He became the Patron St. of Ireland in the 7th Century and we celebrate the date of his death on March 17, with St. Paddy's Day!
In Ireland the day is celebrated as a holy day. Here in America, it has become a celebration of Ireland and all that is Irish.
However you celebrate the day and whatever you are celebrating - I hope you have a Happy St. Paddy's Day!