St Patrick's historicity is not in doubt. He throve in the 5th Century AD. His exact dates are uncertain and there are many legends about him.
As a sideline, many people do not know that English only started to become the predominant language in Ireland in the 19th Century. Before that Irish, a Celtic language was spoken. It is still spoken in parts of the country today and is an official language of Ireland. That is why some Irish names look so strange.