Patrick was born either in England, Wales, or France [depending upon which historical account one finds most credible] of Roman parents sometime during the fifth century a.d. He was kidnapped and sold into slavery and that is how he got to Ireland "the first time." At the age of 16, he was forced to be a shepherd. It is said that a dream he had helped him escape from Ireland around the age of 22 or 26. He then studied for the priesthood [uh, maybe] at any rate he was studying something somewheres or other for a bit until a vision or hallucination or dream told him to go back to Ireland. Patrick was given his name Patricus during his ordination or something. Again, depending upon preferences for which sources, Patrick was either affiliated with the Roman Catholics, the ancient Church of England, the Baptists, or none of the above. The idea that he explained the trinity using a shamrock is crap-- the shamrock symbol for the trinity didn't come about for a thousand years or so after his death. There were no snakes in Ireland. The "snakes" he drove out might or might not be [or might have come about later as] a reference to the spiritual takeover of Ireland by the Roman Catholics or the other christians around [again depending upon who you believe]. He was not the first with a missionary bent to arrive upon the druidic Irish shores.
He might have died on March 17th or he might not have. At any rate, the Roman Catholic Church and the Eastern Orthodox Church both recognize the date as one to celebrate the conversion of pagan Ireland to their version of christianity. Yes, I will be wearing a snake on that day this year. Not because "our spiritual ancestors were killed." Rather, because we pagans and heathens continue to survive in spite of ugly rumors about us and our beliefs and our lifestyles.