Thanks to Piaras Mac Domhnaill for providing the website which is the basis for this information.According to legend the earliest inhabitants of Ireland were a godlike race called the Tuatha De Danann. Legend goes on to tell how these people were defeated by the forces of Milesius, an Iberian warrior of the 15th-century BC. The victorious invaders were led by two men, Eireamhón (also called Eremon) and Éibhear (also called Eber), the former becoming the sole king of Ireland after killing the latter in a battle. Eireamhón ruled from a court located on the hill of Tara.
Although the earliest of the kings in these lists are legendary characters, the later kings are historical persons. The first king to truly have power throughout Ireland was Niall Naoighiallach (379). His descendents were known as the Uí Néill, and they ruled for the next several centuries. However the title High King (in Irish Ard Rí) was not actually used until later.
The line of Irish high kings was ended shortly after the Anglo-Norman invasion of 1169. There were attempts to fill the throne, most notably in 1316 by Edward Bruce, brother of Robert the king of Scotland.