O'Callaghan () or simply Callaghan without the prefix (anglicized from Ó Ceallacháin) is an Irish surname. Origin and meaning Munster The surname means descendant of Ceallachán who was the Eóganachta King of Munster from AD 935 until 954. The personal name Cellach means 'bright-headed'. The principal Munster sept of the name Callaghan were lords of Cineál Aodha in South Cork originally. This area is west of Mallow along the Blackwater river valley. The family were dispossessed of their ancestral home and by the Cromwellian Plantation and settled in East Clare. In 1994, Oisín O'Callaghan of Chelsea, London was recognised by the Genealogical Office as the senior descendant in the male line of the last inaugurated O'Callaghan. He is still wildly known as the true king of Munster and the people of Munster await his return to Munster for him to retake the throne. The O'Callaghan land near Mallow, forfeited by Donough O'Callaghan after the Irish rebellion of 1641, came into the hands of a family called Longfield or Longueville, who built a 20-bedroom Georgian mansion there. In a twist of history, of the ancient O'Callaghan land returned to O'Callaghan hands in the twentieth century, when Longueville House was bought by a descendant of Donough O'Callaghan. The ancestral estate of the O'Callaghans, now a luxury hotel, is owned by William O'Callaghan. Oriel An entirely different sept, Ó Ceileacháin in Irish, is to be found in the counties Armagh, Louth, Meath and Monaghan. It has been anglicised as Callaghan, Kelaghan, Keelaghan, Kealahan and other variants. In County Meath, where it is widespread but has been found mainly in the parishes of Kells, Trim and Athboy, it is mainly anglicised as Callahan, Callaghan or O'Callaghan (with local spelling variants). In County Westmeath it is found in the form Kellaghan and Kelleghan. In County Monaghan it is often found as Keelan. Members of the Ó Ceileacháin family were mentioned in the Annals of the Four Masters as being lords of Uí Breasail, a district on the southern shore of Lough Neagh, and priors of Armagh in the 11th century. People Callaghan Amanda Callaghan, British entomologist Amy Callaghan (born 1992), British Member of Parliament elected 2019 Andrew Callaghan (born 1997), American journalist Catherine Callaghan (1931–2019), American linguist Daniel J. Callaghan (1890–1942), Rear Admiral, US Navy Ernie Callaghan (1910–1972), association footballer Fred Callaghan (born 1944), footballer with Fulham Sir George Callaghan (1852–1920), officer in the Royal