The O'Neill dynasties of ancient Ireland were descended from an Irish high king known as Neill of the Nine Hostages. For a number of generations, the O'Neill clan supplied the Ard Righ or High King of ancient Ireland.

After the invasion of the Anglo-Normans and the end of the Irish High Kingship, the O'Neills continued as an independent and extremely powerful clan ruling much of Ulster. As the centuries passed, the various Irish princedoms fell to the English one by one, by O'Neill domination of Ulster remained essentially unchallenged. They maintained this power both with their own “kerns” or foot-soldiers (usually armed with long knives and “war darts,” which were essentially huge lawn darts for throwing at your enemies!) and Scottish Highland mercenaries known as “gallowglasses.”

Most Irish chieftains of any power maintained as many gallowglasses as they could afford, because the Scottish warriors were more heavily armed and armored than their Irish counterparts (they wore mail coats and fought with battle axes) and were also considered to be much more fierce.

With the help of both their gallowglasses and their kerns, the O'Neills were able to maintain Ulster as an independent Gaelic princedom until the Elizabethan era. The powerful and ruthless warlord Red Shane O'Neill was even invited to London for a private audience with Queen Elizabeth. In the end, however, the O'Neills were defeated, setting the stage for the Cromwellian conquest and the settlement of large numbers of Scottish and English protestants in Ulster, where their descendants remain to this day.