The högkung (Irish: Ard-na hÉireann RI ) was sometimes historical, sometimes legendary figures who had, or claimed to have had dominion over Ireland.
Medieval and early modern Irish literature portrays an almost unbroken sequence of High Kings, ruling from the Hill of Tara of a hierarchy of lesser kings, stretching back thousands of years. Modern historians believe this system is artificial, built in the 8th century from various genealogical traditions politically powerful groups, and seeks to motivate the current status of these groups by projecting it back to the remote past. 
The concept of national kingship first articulated in the 7th century, but only became a political reality in the Viking Age, and even then not a consistent one.    Although the high Kings’ degree of control varied, Ireland never ruled by them as a politically unified state, as the high king perceived as an overlord exercised suzerainty over, and receive tribute from the independent kingdoms under him. : pp. 40-47
Sacred High Kings
Early Irish kingship was sacred nature. In the early narrative literature a king is a king because he marries the sovereignty goddess, free from blemish, upright symbolic Buada [disambiguation needed] (powers) and avoids symbolicgeasa (taboos).
According to the 7th and 8th century legal areas, a hierarchy of domination and client ship developed from Rí tuaithe (king of a single petty kingdom) byruiri (a Rí was of King several petty kingdom) to an Rí ruirech (a Rí was a provincial of king). (See RI.)
Each king ruled directly only in the context of their own petty kingdom and was responsible for ensuring good government by exercising fir flaithemon(rulers’ truth). His responsibilities included calling his óenach (People’s Assembly), collecting taxes, building public works, external relations, defense, disaster legislation, law enforcement and issue a final judgment.
They land in a petty kingdom held allodially of various fines (agnatic kingroups) of free men. King occupied apex of a pyramid of client ship in petty kingdom. This pyramid has gone from the unfree population in its base up to the heads of noble fine held in immediate client ship of the king. The king therefore deducted from the dominant fine within Cenél (a broader kingroup includes the noble fines for petty kingdom).
The kings of Ulster Cycle are kings in this sacred sense, but it is clear that the old concept of kingship coexisted together Christianity for several generations. Diarmait mac Cerbaill, king of Tara in the middle of the 6th century, may have been the last king to have “married” the country. Diarmait died at the hands of AED Dub mac Suibni; some accounts from the following century states that he died of mythical threefold death is appropriate for a sacred king. Adomnán’s life tells how Saint Columba forecast the death of AED Dub. Same Threefold Death said in a late poem have hit Diarmait predecessor, Muirchertach MACC Ercae, and even the usually pålitligaAnnals of Ulster record Muirchertach death by drowning in a vat of wine.
A second sign of the holy kingdom did not vanish with the arrival of Christianity is the supposed lawsuit between Congal Cáech, king of Ulaid and Domnall mac Aedo. Congal probably was blinded in one eye by Domnall bin, from which his surname Cáech (half blind or strabismus), this injury makes him imperfect and unable to remain high King. The antagonism between Domnall and Congal, more prosaically be at the door of the rivalry between the Uí Néill and kings Ulaid, but that a king would be completely in the body seems to have been accepted at this time.
The operations of the Irish heritage is quite complicated because of the nature of kingship in Ireland before the Norman takeover of 1171. Ireland was divided into several kingdoms, with some kings because allegiance to others from time to time, and succession rules (to the extent they were ) varied.Kings often succeeded by their sons, but often other branches of the dynasty took a turn either by agreement or by force of arms is rarely clear.Unfortunately king lists and other early sources reveal little about how and why a particular person became king.
To add to the uncertainty, the family often edited many generations later to improve an ancestor position within a kingdom, or to put him in a more powerful family. The unsafe practices in local kingship causing similar problems in the interpretation of the legacy of the high kingship.
The högkung was essentially a ceremonial, pseudo-federal overlord (where his supremacy was even recognized), who exercised the real power only within the realm of what he was actually king. In the case of the southern part of the UI Neill, this would have been the Kingdom of Meath (now the counties Meath, Westmeath and part of County Dublin). High Kings from the northern branch ruled various kingdoms in what eventually became the province of Ulster.
In 1002, was the high kingdom Ireland wrested from Mael Sechnaill II in Southern Uí Neill from Briain “Boruma” mac Cennédig Kingdom Munster.Some historians have called this a “usurpation” of the throne.  Others have pointed out that no one had a strict legal right to the kingdom  and Brian “had as much right to the high throne as all Uí Neill and … demonstrated an ability sadly lacking among most of the UI Neill who had preceded him. ” 
Brian was killed in the Battle of Clontarf in 1014. Mael Sechnaill II was restored to the High Kingship, but he died in 1022. From 1022 to Norman takeover of 1171, was the high Kingship held parallel “Kings of the opposition”.
Early Christian High Kings
Even at the time when the law writings were attributed to these petty kingdom was swept away by emerging dynasties of dynamic of Kings. The most successful of these early dynasties were Uí Neill (includes descendants of Niall of the Nine Hostages such Cenél Eoghain) that as kings Tara had to conquer petty kingdom, expelling their rulers and agglomerating their territories under the direct rule of their expanding family since the fifth century.
Domestic and foreign, pagan and Christian ideas comingled to form a new idea of Irish kingship. The person the idea of a sacred kingship was integrated with the Christian idea of the coronation ceremony, was the relationship between the king to the king over one of tigerna (master) to the king andempire (sovereignty) began to merge with Dominium (ownership).
The church was well located to the idea of a strong political authority. Its priests developed the theory of a high kingship of Ireland and signed a contract that calls kings to rule rather than reign. In return paruchiae(monastery covenant) of the Irish church had royal patronage in the form of shrines, construction, land and protection.
The concept of a high king sometimes into various annals, such as a series of death Máel Sechnaill mac Maele Ruanaid of 862 in the Annals of Ulster, which lists him as Rí Érenn uile (king of all Ireland), a title that his efterträdareAed Finliath apparently never granted. It is unclear what the political reality behind this title. 
Later High Kings
By the twelfth century the dual process of agglomeration of territory and consolidation of kingship saw the handful of remaining land kind kings abandoning the traditional royal sites for cities, employing ministers and governors, receiving advice from a oireacht (a body of noble counselors), chairman reform synods and maintaining standing armies.
Early royal consequence had the correspondence between the lateral branches of the wider dynasty but succession was now limited to a series of father / son, brother / brother and uncle / nephew inheritance within a small royal fine marked by an exclusive name.
These compact families (the Uí Briain of Munster, the Meic Lochlainn in the north, the UI Conchobhair of Connacht) marriage and competed against each other on a national basis, so that on the eve of the Anglo-Norman invasion of 1169 agglomeration / consolidation process was completed and the regional kingdoms split, cut and converted into fiefdoms held by (or rebel against) one of them acting as king of Ireland.
- List of högkung
- Jump up ^ Dáibhí Ó Cróinín “Ireland, 400-800”, in Dáibhí Ó Cróinín (ed.), A New History of Ireland 1: Prehistoric and Early Ireland , Oxford University Press, 2005, pp 182-234 ..
- Jump up ^ Koch, John T. (2006). Celtic culture: A Historical Encyclopedia. ABC CLO.
- Jump up ^ Roe, Harry; Ann Dooley (1999). Tales of the Elders of Ireland.Oxford University Press.
- Jump up ^ Michael Roberts; et al. (1957). Early Irish history and pseudo-history. Bowes & Bowes Michigan University Press.
- ^ Jump up to: ab Francis John Byrne, Irish Kings and High Kings , London, 1973
- Jump up ^ Revd. Dr. JH Todd, Cogadh Gaedhel re Gallaibh , London, 1867
- Jump up ^ Roger Chatterton Newman, Brian Boru, King of Ireland , Dublin, 1983
- Jump up ^ “The Annals of Ulster”. Ucc.ie. Retrieved 23 May 2012.
- Lebor Gabála Érenn
- Geoghegan Clan
- John Francis Byrne, in 1973, Irish Kings and High Kings , Dublin
- Annals of the Four Masters
- Geoffrey Keating, 1636, Foras Feasa s Éirinn
- High King Niall: the most fertile in Ireland,
- Times Online Times, January 15, 2006
- Laoise T. Moore, et al.,
- The Y chromosome signature hegemony in Gaelic Ireland Am. J. Hum. ,. Genet 78 : 334-338, 2006