Happy St. Patrick's Day!
St. Patrick is one of the patron saints of Ireland, but he was actually of Romano-British descent. His name was originally Maewin Succat and he lived in Britain during the 5th century AD. As a teenager, he was captured by pirates and taken to Ireland where he was forced to work as a slave tending sheep for many years.
Eventually he escaped from Ireland and returned to his home and family in Britain. The many years spent praying in captivity brought him to the priesthood, and he took the name Patrick when he was ordained. Years later he became a bishop, and was sent to Ireland as a missionary. There he used his knowledge of the language and customs to establish churches and convert heathens to Christianity.
Shamrocks are associated with St Patrick because he is purported to have used them as a way to explain the concept of the Holy Trinity (Father, Son, Holy Spirit) to potential Christian converts.
Another legend about St Patrick is that he drove all the snakes out of Ireland. There are no fossil records of snakes in Ireland, so it is more likely that glaciers and cold weather kept snakes away.
"I prayed in the woods and on the mountain, even before dawn. I felt no hurt from the snow or ice or rain."
~ from the writings of St. Patrick