The person who was to become St. Patrick, the patron saint of Ireland, was born in Wales about AD 385. His given name was Maewyn, and he almost didn't get the job of bishop of Ireland because he lacked the required scholarship.
Far from being a saint, until he was 16, he considered himself a pagan. At that age, he was sold into slavery by a group of Irish marauders that raided his village. During his captivity he became a Christian and adopted the name Patrick.
He escaped from slavery after six years and went to Gaul where he studied in the monastery under St. Germain, bishop of Auxerre for a period of twelve years. During his training he got the notion that his calling was to convert the pagans to Christianity.
His wishes were to return to Ireland, to convert the native pagans to Christianity. But his superiors instead appointed St. Palladius. But two years later, Palladius transferred to Scotland. Patrick was then appointed as second bishop to Ireland.
Patrick was quite successful at winning converts. And this fact rightfully upset the Celtic Druids, who had their own native religion. Patrick was arrested several times, but escaped each time. He traveled throughout Ireland, establishing monasteries across the country. He also set up schools and churches which would aid him in his indoctrination of the Irish country into Christianity.
His mission in Ireland lasted for thirty years. After that time, Patrick retired to County Down. He died on March 17 in AD 461. That day has been commemorated as St. Patrick's Day ever since.