The Gallagher (Irish: Ó Gallchobhair) family of County Donegal, formerly one of the leading clans of Cenél Conaill, and therefore of all Ulster, originated in the 10th century as a derivative of their progenitor Gallchobhar mac Rorcain, senior-most descendant of Conall Gulban, son of Niall Mór Noigíallach (Niall of the Nine Hostages).

[5] Genetic analysis of Gallagher Y chromosome haplogroups can trace back their origin to a single medieval, 5th-century individual, lending credence to the legend of Niall Noígiallach.

[9] 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.

The chieftains of his line ruled in relative peace[dubious – discuss] for several generations until the beginning of the Viking invasion of Ireland in the 9th century.

The ruling chieftain of the time, whose real name is not recorded, was almost certainly obliged[dubious – discuss] to come to some accommodation with the foreign invader resulting in the nickname "Gallcóbhair" which has been applied to his descendants thereafter.

Despite the legend that Brian Boru was somehow responsible for the widespread implementation of this naming system, the custom may have developed of its own accord as the Irish population grew in size.

[11] The Ó Gallchobhair sept claims to be the most senior family of the Cenél Conaill as Gallchobar was descended from Conall Gulban.

[12] Although generally aligned with the O'Donnells during the period, a renegade band of Gallaghers helped their rival, Shane O'Neill, escape after the Battle of Fearsaid Suili in 1567.

To maintain their lands and power, the Ó Donnell Lord of Tír Conaill, was forced to recognise Henry VIII as King of Ireland, leader of the Irish Church and had to defend the new English religion from anyone who would advocate papal authority.

It appears that, with the death of the subservient Ó Donnell lord, the practice of Catholicism was left to continue peacefully in Tír Conaill, at least up to the end of the Nine Years' War (c. 1594) and the British Plantation of Ulster (1606).

His attacks on landowners were especially widely known and, in one reported incident, Gallagher and his men raided the home of an extremely unpopular landlord in Killasser and forced him to eat half a dozen eviction notices he had recently drawn up for nearly half a dozen tenant farmers before escaping with silver and other valuables.

Although successfully evading British patrols for some time, he was finally apprehended by authorities in the parish of Coolcarney (or possibly Attymass) near the foothills of the Ox Mountains while recovering from an illness at a friend's home during Christmas.

Immediately sending for reinforcements from Ballina, Castlebar and Swinford, a force of 200 redcoats were sent after Gallagher and, upon their arrival, proceeded to surround the home where the highwayman had been staying.

[20] Frank is most well known for penning Four Glorious Years 1918–1921[21] and becoming the deputy director of the first Dáil's Department of Publicity in March 1921, assisting his colleague Erskine Childers, and together they published the Irish Bulletin.

The correct heraldic blazon is "Argent, a lion rampant Sable, treading on a serpent in fess Proper, between eight trefoils Vert.