St. Patrick, if he existed, was a Germanic invader kidnapped from the coast of England by Irish clansmen and taken back to Ireland as a slave. He escaped, fled back to England, became a follower of the Roman Catholic Church, and then eventually went back to Ireland to convert the heathens, either because having spent time with them he felt a need to convert the Irish and "help" them, or because he was mad at them impinging on his liberty for years and wanted revenge. Given his next actions, I'm inclined to go with the latter motive.
Over several years, St. Patrick travelled across Ireland "converting" people. In most cases this involved inciting people to riot and kill one another until only the righteous remained. In one case he took a kid, put his cloak on the kid, put the cloak of a Druid on himself (the last bit of which makes no sense as the Druids tended to run things out of England, not Ireland), then set a building on fire and took them both inside. The story goes that only the Druid's cloak burned, because Druids are evil, but St. Patrick survived 'cause he was holy, but the kid was safe because he was wearing Patrick's cloak. Say it with me now: UH?
His other exploits involved ending drought, dismantling hundreds-of-years-old kingship systems in favour of Christian servitude, and driving fictional snakes from Ireland from the peaks of fictional mountains (Here is where I should note that even if there are peaks in Ireland that could be called mountains - a fact I'd dispute, but I admit based mostly on the fact that I'm a British Columbian and therefore rather snooty about my mountains - THERE HAVE NEVER BEEN ANY SNAKES, ASK A BIOLOGIST, SO THERE. Ireland is an island, which means that if there never *were* any snakes, there can't have *evolved* any snakes and I just realised that I brought evolution into a discussion on Catholic myth. Never mind.), and many mytho-historians blame St. Patrick for delivering Ireland into the at-the-time incompetent hands of the British, after managing to avoid even being invaded by Rome.
So, yeah. St. Patrick is a load of hooey.
On the other hand, St. Patrick's Day is the only really international Celtic holiday I can think of (even if some people claim it does perpetuate a negative stereotype of Celts which, if my family is any metre-stick, is not an altogether, completely, 100% inaccurate one ;), so on that count, more power to them.
It is also smolder's birthday, which is a Good Thing. Happy Birthday, smolder! Hope you have a good one.