Today is St. Patrick's Day, which is a holiday composed entirely of legends and misreadings of history.
St. Patrick, who was probably born in Wales, the son of a Roman official, was historically a missionary in Ireland in the fifth century; a lot of the stories about him were probably stolen completely from the life of Palladius (sent by Pope Celestine I as the first bishop to Irish Christians in 431 CE or so). Paddy himself was supposed to have lived from about 387 CE until 17 March, 493 CE. Since damned few people lived to be 106 in those days (or these, for that matter), that's probably wrong.
The legend says that our boy Paddy drove the snakes out of Ireland. Since the fossil record is pretty clear that there weren't any snakes in Ireland after the last Ice Age, that legend isn't very likely. He was also supposed to have used the 3-lobed shamrock to teach about the Holy Trinity, but there's no real evidence that he did.
He's said to be buried, along with St. Brigid and St. Columba, at Down Cathedral in Downpatrick, County Down (notice a pattern there?). Nobody is has ever been able to prove it, of course.
The "wearin' o' the green" is one of the primary traditions around St. Patrick's Day. Until the 17th Century, the color associated with Paddy was blue, but then politics came into the mix.
The holiday was pretty much restricted to Ireland until the 1600's, when a scholar named Luke Wadding got it inserted into the catholic liturgical calendar. In most of the world, St. Patrick's Day is just an opportunity to get drunk, but since the Roman Catholic church is well-known for sucking the fun out of anything, it's long been a holy day of obligation in Ireland.
(Irish MP James O'Mara got St. Patrick's Day to be an official holiday in Ireland in 1903; later, when the drinking got out of hand, O'Mara got a law closing the pubs on St. Patrick's Day passed. That one was only repealed in the 1970's.)
The first St. Patrick's Day Parade in the world was held in Boston on 18 March 1737, and was primarily a political statement by Irish immigrants, who were upset with their low social status and the fact that nobody would hire an Irishman. (The first St. Patrick's Day Parade in Ireland wouldn't be held until 1931.)
George Washington set up what's now known as the St. Patrick's Day Encampment of 1780, "as an act of solidarity with the Irish in their fight for independence." (So, mostly just to stir up trouble for the British.)
The first St. Patrick's Day Parade in New York was held in 1762 by Irish soldiers in the British Army, so that wasn't real popular. The first American celebration in New York was in the Crown and Thistle Tavern, in 1766, and the parades were again held to draw attention to the plight of the Irish immigrant. Over the years, the New York parades have become the largest in the world. (In case you're curious, the shortest traditional St. Patrick's Day Parade is held in Dripsey, in County Cork, Ireland, and runs about 100 yards. From one of the town's two pubs to the other one.)
Then, during the Irish Rebellion of 1798, the United Irishmen wore all-green uniforms on March 17th, apparently just to draw attention to themselves.
The "traditional" meal of corned beef and cabbage is an American invention; the actual Irish tradition was to eat bacon and cabbage, but the bacon was too expensive. The Irish immigrants went for the cheaper corned beef made by their Jewish neighbors.
The tradition of puking up green beer is, according to the researches of the son of one bar owner started 75 years ago, in Iowa City, Iowa. (A lot of bartenders hate green beer, by the way. It stains the beer lines, and your beer runs cloudy and slightly khaki for the last few weeks of March.)
So overall, there really isn't a lot of truth to anything about this holiday. Of course, when you're drunk, does it really matter?
Happy St. Patrick's Day.