The habit of prefixing the family name with O’ or Mac is one of the most identifying characteristics of Irish surnames. This is also one of the most common prefixes. Hereditary surnames were introduced in Ireland at an early date, making it one of the pioneering nations in this regard. It is thought that many of these were developed during the time of Brian Boru, who was the High King of Ireland. They are used to this very day in many different contexts.