Although the haze of history conceals much about St. Patrick, this much is known: He was not even Irish. He was born in Roman Britain and kidnapped by Irish attackers and made a slave. After escaping captivity, Patrick returned to Britain and became a priest, and later a bishop. He returned to Ireland 30 years later and was a Christian witness among the Irish, converting thousands.
March 17th, popularly known as St. Patrick’s Day, is believed to be the day he died and is the date celebrated as his feast day. St. Patrick has never been formally canonised by a Pope; however, various Christian churches declare that he is a Saint in Heaven.
How we got from there to green beer is up for speculation.