In 432, it was St. Patrick who converted Ireland to Christianity. When trying to explain the Holy Trinity to King Laoghaire, St. Patrick made use of the shamrock to illustrate the Trinity.
There is a legend that St. Patrick drove all the snakes out of Ireland. Actually, there never were any snakes in Ireland. What the legend really refers to is thge symbolism of snakes as pagnanism. St. Patrick actually drove out the paganism from Ireland.
St. Patrick dies on March 17, 461 at the age of 76.
The first American celebration of St. Patricks Day was in 1937 at Boston. The Irish heritage has a profound influence in our nation. Nine of the people who signed the Declaration of Independence were of Irish origin and nineteen presidents of the United States are of Irish heritage, including George Washington.
As for the tradition of eating corned beef and cabbage, well, that started in the U.S. around the turn of the century. The Irish tradition is to eat boiled bacon and cabbage.