sdandrea1 He was actually abducted into slavery in Ireland, then escaped back to his own country.
Eventually he decided that he could fix Ireland by bringing them Christianity. He lived out the rest of his days there. He was never officially canonized, which is why, technically at least, he isn't a 'saint' in the traditional meaning of the word.
But he did have a huge impact on Ireland and was well known and revered for his work there.
Not sure why we have a day to celebrate Irish culture but not one for German or French or Italian or fill-in-the-blank-here, but i suspect it has something to do with Irish-American immigrants.
There were St Patrick's Day parades in Savannah, GA decades before they had them in Dublin. America gave birth to St Patrick's Day, not Ireland.