Wikipedia: Gallowglass
“The gallowglass were an elite class of mercenary warrior who came from Norse-Gaelic clans in the Hebrides and Highlands of Scotland between the mid 13th century and late 16th century.”
“They were the mainstay of Scottish and Irish warfare 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.”