St. Patrick of Ireland

...was not Irish. He was a British Celt, first enslaved in Ireland as a teen, later a missionary to Ireland.
...was not necessarily the first missionary to Ireland.
No one knows his birth or death date. 17 March is traditionally considered to be one of the two, but there is no documentation for this. He probably lived sometime between the later part of the fourth century to the end of the fifth century, A.D.
The only documents about Patrick are his Confession and a letter he wrote to Coroticus.
There were never snakes—or other reptiles—in Ireland for Patrick to chase out.
Patrick's status as a Saint predates the centralized practice of the Roman Catholic Church, being considered a Saint before the Roman church created its canon (list) of saints (and added him to it).

The Confession

...contains approximately 200 references to scripture.
...contains The Rule of Faith of the Trinity, a creed of the ancient Celtic Church.

...is attributed to Patrick, but may not be written by him.
...is found in many variations. Some leave out the middle section, some have only the middle section, and some are more or less like what you see here. This version is an example that contains all the verses that are normally associated with the shield, which is also sometimes called the breastplate of St. Patrick.

This translation appears to be in the public domain, but please be polite and attribute the source (Ludwig Bieler, not me!) if you use it in any way.

This document and many others like it may be found in the Christian Classics Ethereal Library server, at Wheaton College.