Gallowglass

This is a period I know nothing about but the below reenactment group have made me curious about this part of Irish history.
Wiki entry here. It starts with

The gallowglass were a mercenary warrior elite among Gaelic-Norse clans residing in the Western Isles of Scotland (or Hebrides) and Scottish Highlands from the mid 13th century to the end of the 16th century. As Scots, they were Gaels and shared a common origin and heritage with the Irish, but as they had intermarried with the 10th century Norse settlers of the islands and coastal areas of Scotland and the Picts, the Irish called them Gall Gaeil ("foreign Gaels").

They were the mainstay of Scottish and Irish warfare before the advent of gunpowder, and depended upon seasonal service with Irish lords. A military chieftain would often select 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.