The gallowglass or galloglass (also spelt gallowglas or galloglas) – from Irish: gallóglaigh (plural), gallóglach (singular) – were a class of elite mercenary warriors who principally were members of the Norse-Gaelic clans of Scotland between the mid 13th century and late 16th century. As Scots, they were Gaels and shared a common background and language with the Irish, but as they had intermarried with the 10th century Norse settlers of western Scotland, the Irish called them Gall Gaeil ("foreign Gaels").
Large numbers of gallowglass septs settled in Ireland after being dispossessed of their lands in Scotland for choosing the wrong sides in the Wars of Scottish Independence. The first and probably most famous of these were the MacSweeneys, (who unlike most were said to be of native Irish ancestry) settled originally by the O’Donnells in west Donegal. These were followed by MacDonnells, MacCabes and several other groups settled by powerful Irish nobles in different areas. The gallowglass were attractive as a heavy armour trained aristocratic infantry to be relied on as a strong defence for holding a position, unlike most Irish foot soldiers, who were lower class and less well armoured than the typical Irish noble who fought as cavalry. In time there came to be many native Irish gallowglass as the term came to mean a type of warrior rather than an ethnic designation.
They were a significant part of Irish infantry before the advent of gunpowder, and depended upon seasonal service with Irish chieftains. A military leader would often choose a gallowglass to serve as his personal aide and bodyguard because, as a foreigner, the gallowglass would be less subject to local feuds and influences.