O'Mahony, the most common contemporary form of the name, comes from the Irish O' Mathghamhna clan,stemming, like
MacMahon, from mathghamhan, meaning 'bear'. The surname was adopted in the eleventh century by one of the dominant
families of the Munster Eoghanacht peoples, the Cineal Aodha; the individual from whom the name derives was the child of a
marriage between Cian, chief of the Cineal Aodha, and Sadhbh, daughter of Brian Boru. With the rise of the MacCarthys in the
twelfth century the influence of the O'Mahonys declined, and was largely confined to the two areas of west Cork with which
they are still most strongly associated, the Iveagh peninsula and the barony of Kinalmeaky, around the modern town of Bandon.
In these areas they retained a large measure of power and wealth until the final collapse of Gaelic power in the wars of the
seventeenth century. The most famous modern bearer of the name was Eoin ('the Pope') O'Mahony (1904-1970), barrister
and genealogist, who preserved and interpreted with accuracy and enthusiasm the traditions of his own and many other families,
founding and organising the annual clan gathering of the O'Mahonys.