At least 30 recorded alternate variants exist, including O'Gallagher, Gallacher, Gallager, Gallaher, Gallocher, Galliher, Gollaher, Gollihar and Gallahue.
A similarly earlier mention occurs in the Annals of the Four Masters, where it is recorded that Mael Cobo Úi Gallchobhar, Abbot of Scrin Adamnain, died in 1022 AD.
Gallchobhar was the one given the role of founding father of the clan at the advent of widespread surname usage in Ireland, which began around the 10th century.
As with other modern Irish last names, Ó Gallchóir similarly appears to be a conjoined compound word.
[2] According to Professor Edward MacLysaght, in the mid-20th century Gallagher was one of the most common Irish surnames, most of the recorded births being located in the northern province, Ulster, and the western province, Connacht, with the majority being recorded in the homeland of the sept—County Donegal in Ulster.