Compared to St Valentine, we know quite a lot about St Patrick. Perhaps too much in fact. The Annals of Ulster suggest he was born in 340, began preaching in Northern Ireland in 428 and died in 440 (on 17 March), a lifespan that strains credibility. Historians tend towards the "Two Patricks" theory which suggests that two real missionaries were conflated into one legendary figure
Interestingly, there are two documents generally accepted as written by Patrick. One of them, his confession, describes his life, starting as a highborn Roman, being carried off as a slave by Irish raiders, his escape, joining St Germain in an expedition to Britain to stamp out heresy and finally as missionary to Ireland. Exciting stuff!
Strangely none of this mentions black beer, leprechauns or banishing snakes from Ireland. As well as Ireland, Patrick patronises all kinds of snake related fears, engineers, the excluded and Nigeria.
 Or even green