According to an article by Laurel A. Rockefeller, "Saint" Bishop Patrick as we think of him is far more myth than history.
In March, 2012 she researched Bishop Patrick and concluded that most of what we think we know about this man who, we are told, banished serpents from Ireland, is almost entirely myth. Working from two sources collecting period texts, she theorizes that the real Patrick reveals himself as a Breton who was, typical of his time, abducted by an Irish raiding party and sold into slavery, setting him onto a life-long path of anti-Irish resentment. Contrary to what was written about him after his death, the article finds that Patrick's motives for going to Ireland to preach were far more rooted in his animosity towards the Irish than we were previously led to believe.
The full article can be found at the first link below; the other two links go to the above-mentioned cited references.