Recorded in various forms including Galagher, Gallagher, and the unusual dialectal Callacher, this is an Irish surname. It derives from the medieval Gaelic name of O' Gallchobhair, the prefix O' indicating "male descendant of", plus the personal byname "Gallchobhair", a compound of the elements "gall", meaning foreign, and "cabhair meaning help. This may may have indicated that the clan were originally foreign mercenaries. The O' Gallaghers belonged to County Donegal, and are of the Cineal Connaill line. That is to say one of the families descended from Connall Gulban, son of Niall of the Nine Hostages, a 4th century king of Ireland. Their identifying name was possibly acquired during the 14th century when their chiefs were marshals in the O'Donnell military forces which held possession of Donegal, although this seems rather late. The name as Gallagher is the fourteenth most numerous in Ireland, and is chiefly found today in the provinces of Ulster and North Connacht. Several namebearers were noted ecclesiastics including the most Reverend Redmond O' Gallagher (1521 - 1601), a bishop of Derry who was martyred for the aid he rendered to survivors of the Spanish Armada. The first recorded spelling of the family name is shown to be that of Teag O' Gallchobhair, which was dated 1350, in the Ancient Records of Tirconnell, Donegal. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.