The clan hails from the barony of Tirhugh ("land of Hugh") near Ballyshannon, County Donegal, Ireland.
The derivation of the surname Gallagher is "foreign help" or "foreign helper" from the Irish gall meaning "stranger" and cobhair meaning "help". It is a matter of conjecture whether this appellation denoted merely an ally of strangers from other parts or, as has been suggested, more particularly a collaborator with the Norsemen, who were in those days raiding the coast of north west Ireland. The family's origins are with the chieftain Aodh, a name corresponding to the English Hugh (whence Tirhugh), a lineal descendant of Conall Gulban son of 5th century High King and warlord Niall Noígíallach, known in English as Niall of the Nine Hostages, who is reputed to have brought St Patrick to Ireland as a slave. Aodh established his dunarus or residence at a place corresponding to the present day townland of Glassbolie in Tirhugh. The chieftains of his line ruled in relative peace for several generations until the arrival of the Vikings in Donegal Bay in the 9th century. The ruling chieftain of the time, whose real name is not recorded, was almost certainly obliged to come to some accommodation with the foreign invader resulting in the nickname "Gallcóbhair" which has been applied to his descendants thereafter.
The Gallagher coat of arms displays a black lion rampant on a silver shield, treading on a green snake surrounded by eight green trefoils. The correct heraldic description is "Field argent a lion rampant sable treading on a serpent in fess proper between eight trefoils vert". The crest which surmounts the helmet over the shield depicts a red crescent surrounding a green snake or, to give its heraldic definition, "A crescent gules out of the horns a serpent erect proper". The motto of the clan is in Latin Mea Gloria Fides ("The Faith is My Glory").[5]
