According to Irish tradition, the ancient Kings of Ireland were the descendants of King Milesius of Spain. Milesius was the grandson of Breoghan, conqueror of Galicia, Andalusia, Murcia, Castile, and Portugal, who was also called Brigus or Brian. Milesius achieved outstanding military success in Egypt, and was given Scota, the Pharoah's daughter, in marriage. When Spain underwent a twenty-six year famine, Milesius sent his uncle Ithe to seek a new homeland, in accordance with an ancient prophecy. After Ithe discovered Ireland, only to be murdered by the resident Tuatha de Danan, his son Lughaide brought his body home to Spain.
In vengeance, Milesius sent his eight sons with a great fleet to conquer the lush green isle. Along the way, a vicious storm claimed the lives of five of the sons, including Ir, whose son Heber-Donn survived. Landing on the island in 1699 BC, the remaining three sons, Heremon, Heber, and Amergin, slew the Danan kings with the aid of Heber-Donn. Heber and Heremon divided the land between them and ruled as joint kings, calling the land 'Scotia', after their mother, and giving lands to Lughaide and Heber-Donn.
However, after only one year, a disagreement between their ambitious wives sparked a war between the brothers; Heremon slew Heber and then the childless Amergin and became sole king of Ireland. Tradition dictates that almost all the ancient kings of Ireland descended from Heremon, Heber, Ir and Ithe.
Among these royal descendants were several famous kings. These include Conn of the Hundred Battles, who was so called due to the hundreds of military victories he achieved during his lengthy 2nd century reign, which ended when he was assassinated by fifty thugs disguised as women. The Three Collas were brothers who were banished from Ireland in the 4th century after being usurped as monarchs by the son of the uncle whom they had previously overthrown. Exiled to Scotland for thirty years before their eventual pardon, they took the name 'Scotia' with them, transferring it to that land. Ireland was subsequently renamed in honor of Ir, brother of Heber and Heremon.
Later in that century, Ireland was ruled by King Niall of the Nine Hostages Niall Noígíallach (birth and death dates - circa 4th and 5th century), whose military exploits are said to have made those of King Arthur pale by comparison. Defeating the Romans in Gaul and Britain, he prevented a Roman conquest of Ireland and gained his name from his habit of taking important captives from each of the nine nations he conquered during his career. His reign of Ireland differs with each reference consulted. The Annals of the Four Masters dates his accession to 378 and death at 405. Laeghaire MacNiall became the first Christian Monarch of Ireland.
The most celebrated of all Irish kings was Brian Boru (c. 941-1014), who tradition credits with the introduction of hereditary surnames to Ireland. He deposed Malachi II as Monarch of all Ireland in 1002 AD, though the succession was amicable and Brian retained Malachi II as a valuable ally. In 1014, the Danes, who already controlled all of England and parts of Ireland, challenged Brian Boru for the leadership of Ireland. Fielding an army composed of forces from the provinces of Munster and Connacht, Brian Boru led the Irish to a decisive victory over the Danes and their allies, permanently ending the Danes' dreams of establishing their supremacy in Ireland. However, Brian Boru was slain in battle, at the age of 88. Malachi II re-ascended the throne, where he ruled as what many consider to have been the last absolute Monarch of all Ireland. After his death, the various provincial kings descended into endless quarreling amongst themselves in futile hopes of ruling the entire nation.