Born c. 396

Died c. 459

Roman-Irish saint

Patron saint of Ireland, St. Patrick remains one of the Middle Ages' most well-known saints, thanks in large part to the wild celebrations on his festival day on March 17. Wherever there are sons and daughters of Ireland—as in America, a country with far more people of Irish heritage than Ireland itself—there is plenty of merry-making on St. Patrick's Day.

Yet it might astound many to learn, first of all, that Patrick was not Irish; rather, he was a missionary, a religious teacher sent to people in a foreign land, from Roman-controlled Britain. Nor was he a particularly jolly figure, despite all the fun associated with his day. Furthermore, many of the feats attributed to him—for instance, driving all the snakes out of Ireland—are the product of medieval legend-making, not fact.

Sold into slavery

Patrick, or...