After six years of slavery he escaped Ireland and returned to his homeland where he became a priest and later a bishop. He then felt a calling to return to Ireland to evangelize the place where he was once a slave.
Initially his work in Ireland was difficult because the Celtic beliefs were so deeply rooted with the people. But St. Patrick went on to found monasteries and spread the Gospel little by little. The tradition of the three leaf clover actually comes the way he used it to explain the Trinity, three persons and one God.
Now, 16 centuries after St. Patrick arrived in Ireland, not only the Irish but the entire world celebrate their patron saint.