King of Ireland:

A monarchical polity has existed in Ireland during three periods of its history, finally ending in 1801. The designation King of Ireland (Irish: Rí na hÉireann) and Queen (regnant) of Ireland was used during these periods. Since 1949, the only part of Ireland that retains a monarchical system is Northern Ireland (as part of the United Kingdom of Great Britain and Northern Ireland).

Gaelic Kings and Kingdoms:

Gaelic Ireland consisted of as few as five and as many as nine main kingdoms, subdivided into dozens of smaller kingdoms. The primary kingdoms were Connacht, Ailech, Airgíalla, Ulster, Mide, Leinster, Osraige, Munster and Thomond. Until the end of Gaelic Ireland they continued to fluctuate, expand and contract in size, as well as dissolving entirely or being amalgamated into new entities. The role of High King of Ireland was primarily titular and rarely (if ever) absolute.

The names of Connacht, Ulster, Leinster and Munster are still in use, now applied to the four modern provinces of Ireland. The following is a list of the main Irish kingdoms and their kings.

Kings of Ailech - divided into Tír Eóghain and Tír Conaill in twelfth century
Kings of Connacht - all the land west of the Shannon except Thomond.
Kings of Leinster - Its last de facto king died in 1632.
Kings of Mide - Ireland's central kingdom, annexed by Connacht in the 11th century.
Kings of Munster - an overkingdom of late prehistoric origins
Kings of Ulster - properly, Ulster east of the lower and upper Bann.

Ard Ri co febressa:High-Kings with Opposition:

Maire Herbert has noted that Annal evidence from the late eighth century in Ireland suggests that the larger provincial kingships were already accruing power at the expense of smaller political units. Leading kings appear in public roles at church-state proclamations ... and at royal conferences with their peers. (2000,p. 62). Responding to the assumption of the title ri hErenn uile (king of all Ireland) by Mael Sechlainn I in 862, she furthermore states that:

... the ninth-century assumption of the title of "ri Erenn" was a first step towards the definition of a national kingship and a territorially-based Irish realm. Yet change only gained ground after the stranglehold of Ui Neill power-structures was broken in the eleventh century. ...The renaming of a kingship ... engendered a new self-perception which shaped the future definition of a kingdom and of its subjects. (Herbert, 2000, p. 72)

Nevertheless, the achievements of Mael Sechlainn and his successors were purely personal, and open to destruction upon their deaths. Between 846-1022, and again from 1042-1166, kings from the leading Irish kingdoms made greater attempts to compel the rest of the island's polity to their rule, with varying degrees of success, until the inauguration of Ruaidri Ua Conchobair (Rory O'Connor) in 1166,

High-Kings of Ireland 846-1198:

Mael Sechnaill mac Maele Ruanaid, 846-860
Aed Findliath, 861-876
Flann Sinna, 877-914
Niall Glundub, 915-917
Donnchad Donn, 918-942
Congalach Cnogba, 943-954
Domnall ua Neill, 955-978
Mael Sechnaill mac Domnaill, 979-1002; 1014-1022
Brian Boruma, 1002-1014
Donnchad mac Briain, died 1064
Diarmait mac Mail na mBo, died 1072
Toirdelbach Ua Briain, died 1086
Muirchertach Ua Briain, died 1119
Domnall Ua Lochlainn, died 1121
Toirdelbach Ua Conchobair, died 1156
Muirchertach Mac Lochlainn, died 1166
Ruaidri Ua Conchobair, died 1198

Ruaidhri, King of Ireland:

Upon the death of Muirchertach Mac Lochlainn in early 1166, Ruaidhri, King of Connacht, proceeded to Dublin where he was inaugurated King of Ireland without opposition. He was arguably the first undisputed full king of Ireland. He was also the only Gaelic one, as the events of the Norman invasion of 1169-1171 brought about the destruction of the high-kingship, and the direct involvement of the Kings of England in Irish politics.

One of Ruaidri's first acts as king was the conquest of Leinster, which resulted in the exile of its king, Dermot MacMurrough. Ruaidri then obtained terms and hostages from all the notable kings and lords. He then celebrated the Oneach Tailtann, a recognised prerogative of the High Kings, and made a number of notable charitable gifts and donations. However, his caput remained in his home territory in central Connacht (County Galway). Ireland's recognised capital, Dublin, was ruled by Hasculf Thorgillsson, who had submitted to Ruaidri.

Only with the arrival of MacMurrough's Anglo-Norman allies in May 1169 did Ruaidri's position begin to weaken. A series of disastrous defeats and ill-judged treaties lost him much of Leinster, and encouraged uprisings by rebel lords. By the time of the arrival of Henry II in 1171, Ruaidri's position as king of Ireland was increasingly untenable.

Ruaidri at first remained aloof from engagement with King Henry, though many of the lesser kings and lords welcomed his arrival as they wished to see him curb the territorial gains made by his vassals. Through the intercession of Archbishop Lorcán Ua Tuathail (Lawrence O'Toole), Ruaidri and Henry came to terms with the Treaty of Windsor in 1175. Ruaidri agreed to recognise Henry as his lord; in return, Ruaidri was allowed to keep all Ireland as his personal kingdom outside the petty kingdoms of Laigin (Leinster) and Mide as well as the city of Waterford.

Henry was unwilling or unable to enforce the terms of the treaty on his barons in Ireland, who continued to gain territory in Ireland. A low point came in 1177 with a successful raid into the heart of Connacht by a party of Anglo-Normans, led by one of Ruaidri's sons, Prince Muirchertach. They were expelled, Ruaidhri ordering the blinding of Muirchertach, but over the next six years his rule was increasingly diminished by internal dynastic conflict and external attacks. Finally, in 1183, he abdicated.

He was twice briefly returned to power in 1185 and 1189, but even within his home kingdom of Connacht he had become politically marginalised. He lived quietly on his estates, and died at the monastery of Cong in 1198. With the possible exception of Brian O'Neill (died 1260), no other Gaelic king was ever again recognised as king or high king of Ireland.

The Lordship of Ireland:1198-1542:

By the time of Ruairi's death in 1198, two English kings, Henry II and Richard I, had exercised rule over the areas inhabited by the Anglo-Normans, and claims of allegiance from various Gaelic kings and lords. Successive kings of England did so as lords of Ireland. By the mid-13th century much of the island was under the direct and/or indirect rule of the king of England, but from c.1260 the size of the actual lordship began to recede, as various families died out in the male line while the Gaelic-Irish began to reclaim lost territory. The problem was recognised as significant at the parliament of 1297, yet successive English kings did little to stem the tide, instead using Ireland to draw upon men and supplies in the wars in Scotland and France.

By the 1390s the king's lordship had effectively shrunk to the Pale with the rest of the island under the control of independent Gaelic-Irish or rebel Anglo-Irish. Richard II of England made two journeys to Ireland during his reign to rectify the situation; as a direct result of his second visit in 1399 he lost his throne to Henry Bolingbroke. This was the last time that a medieval king of England visited Ireland.

For the duration of the 15th century, royal power in Ireland was weak, the country being dominated by the various clans and dynasties of Gaelic (O'Neill, O'Brien, McCarthy) or Anglo-Norman (Burke, FitzGerald, Butler) origin. Affairs closer to London ensured, well into the 1530s, that Irish affairs remained at best a secondary concern.

Lords of Ireland 1171-1541:

Henry II of England, (1171-1189)
Richard I of England, (1189-1199)
John of England, (1199-1216)
Henry III of England, (1216-1272)
opposed by: Brian O'Neill, 1258-1260
Edward I of England, (1272-1307)
Edward II of England, (1307-1327)
opposed by: Edward Bruce, (1315-1318)
Edward III of England, (1327-1377)
Richard II of England, (1377-1399)
Henry IV of England, (1399-1413)
Henry V of England, (1413-1422)
Henry VI of England, (1422-1461 and 1470-1471)
Edward IV of England, (1461-1470 and 1471-1483)
Edward V of England, (1483)
Richard III of England, (1483-1485)
Henry VII of England, (1485-1509)
Henry VIII of England, (1509-1542)

The Kingdom of Ireland:1542-1801:

The title "King of Ireland" was created by an act of the Irish Parliament in 1541, replacing the Lordship of Ireland, which had existed since 1171, with the Kingdom of Ireland. The Crown of Ireland Act 1542 established a personal union between the English and Irish crowns, providing that whoever was king of England was to be king of Ireland as well, and so its first holder was Henry VIII of England. This followed the failure of the plan to make Henry FitzRoy, 1st Duke of Richmond and Somerset, the King of Ireland. Although FitzRoy was made Lord-Lieutenant, the King's counselors feared that making a separate Kingdom of Ireland, with a ruler other than that of England, would create another threat like the King of Scotland. (J.J. Scarisbrick, English Monarchs: Henry VIII, University of California Press)

For a brief period in the 17th century, during the Wars of the Three Kingdoms from the impeachment and execution of Charles I to the Restoration of the monarchy in England, there was no 'King of Ireland' in fact, only in name. After the Irish Rebellion of 1641, Irish Catholics, organised in Confederate Ireland, recognised Charles I and later Charles II as legitimate monarchs, in opposition to the claims of the English Parliament, and signed a formal treaty with Charles I. But in 1649, the Rump Parliament, victorious in the English Civil War, executed Charles I, and made England a republic, or "Commonwealth". The Parliamentarian general Oliver Cromwell came across the Irish sea to quash any attempt to restore the monarchy by temporarily - though illegally - uniting England, Scotland, and Ireland under one government, styling himself "Lord Protector" of the three kingdoms. After Cromwell's death in 1658, his son Richard emerged as the leader of this pan-British-Isles republic, but he was not competent to maintain it. Parliament at London voted to restore the monarchy and Charles II returned from exile in France in 1660 to become King of England, King of Scotland and King of Ireland.

The Acts of Union 1707 merged the kingdoms of England and Scotland into the Kingdom of Great Britain. This entity was also known as the British Crown. The effect was to create a personal union between the Crown of Ireland and the British Crown. Later, on 1 January 1801, an additional merger took place between the two Crowns. By the terms of the Act of Union 1800, the Kingdom of Ireland merged with the Kingdom of Great Britain creating the United Kingdom of Great Britain and Ireland. Following the separation of most of Ireland from that political entity, the remaining constituent parts were renamed the United Kingdom of Great Britain and Northern Ireland in 1927, five years after the establishment of the Irish Free State).

Irish Free State (1927-1936):

In 1922, Ireland left the United Kingdom of Great Britain and Ireland as the Irish Free State (renamed Ireland in 1937), a self-governing Dominion of the British Empire. However and within a few days, Ireland's six northeastern counties opted to rejoin the UK as Northern Ireland, leaving the Free State with 26 counties. As a Dominion, the Free State was a constitutional monarchy with the monarch as its head of state.

The King's title in the Irish Free State was exactly the same as it was elsewhere in the British Empire, being:
From 1922 to 1927 - By the Grace of God, of the United Kingdom of Great Britain and Ireland and of the British Dominions beyond the Seas King, Defender of the Faith, Emperor of India
From 1927 to 1937 - By the Grace of God, of Great Britain, Ireland and the British Dominions beyond the Seas King, Defender of the Faith, Emperor of India

The change in the King's title was effected under an Act of the Parliament of the United Kingdom called the Royal and Parliamentary Titles Act, 1927. The Act was intended to update the name of the United Kingdom as well as the King's title to reflect the fact that most of the island of Ireland had left the United Kingdom. The Act therefore provided that:
"It shall be lawful for His Most Gracious Majesty by His Royal Proclamation under the Great Seal of the Realm, issued within six months after the passing of this Act, to make such alteration in the style and titles at present appertaining to the Crown as to His Majesty may seem fit";
"Parliament shall hereafter be known as and styled the Parliament of the United Kingdom of Great Britain and Northern Ireland" (instead of the Parliament of the United Kingdom of Great Britain and Ireland);
"In every Act passed and public document issued after the passing of this Act the expression "United Kingdom" shall, unless the context otherwise requires, mean Great Britain and Northern Ireland."

According to The Times the "Imperial Conference proposed that, as a result of the establishment of the Irish Free State, the title of the King should be changed to "George V, by the Grace of God, of Great Britain, Ireland, and the British Dominions beyond the seas King, Defender of the Faith, Emperor of India." The change did not mean that the King had now assumed different Styles in the different parts of his Empire. That development did not formally occur until 1953, four years after Ireland had left the Commonwealth.

Irish Free State / Ireland (1936-1949):

From 1936 to 1949 the role of the King in the Irish Free State was greatly reduced and ambiguous. An amendment to the Constitution of the Irish Free State in 1936 eliminated all but one of the King's official duties. Under the External Relations Act of the same year he continued to represent the Free State in international affairs. This purely external role continued when the new Constitution of Ireland was introduced in 1937.

The position of the King in the Irish state ended with the Republic of Ireland Act 1948, which came into force in April 1949. This Act repealed the External Relations Act and declared the state was a republic. The Crown of Ireland Act was formally repealed in the Republic of Ireland by the Statute Law Revision (Pre-Union Irish Statutes) Act, 1962.

The monarchy continues in Northern Ireland, which remains a part of sovereign state of the United Kingdom of Great Britain and Northern Ireland.

Monarchs of Ireland:
Ruaidri Ua Conchobair, inauguraged at Dublin, spring 1166. Died 1198. He was the last native to be widely recognised as monarch of Ireland.
Henry VIII of England (1542-1547); Lord of Ireland, (1509-1542)
Edward VI of England, (1547-1553)
disputed claimant: Lady Jane Grey, (1553)
Mary I of England, (1553-1558)
Philip II of Spain, jure uxoris (1554-1558)
Elizabeth I of England, (1558-1603)
James I of England, (1603-1625) (James VI of Scotland, I of England and of Ireland). He held all three crowns in a personal but not a political union.
Charles I of England, (1625-1649)

Interregnum:

Charles II of England, (1660-1685)
James II of England, (1685-1688)
William III of England, (1689-1702) & Mary II of England, (1689-1694)
Anne of Great Britain, (1702-1714)

Monarchs of the Kingdom of Great Britain and of the Kingdom of Ireland:

Anne of Great Britain, (1702-1714) Following the Act of Union with Scotland, Anne's personal union of the Scottish and English crowns was replaced by a political union. The united entity was known as the "United Kingdom of Great Britain". The personal union with the crown of Ireland was still in place.
George I of Great Britain, (1714-1727)
George II of Great Britain, (1727-1760)
George III of Great Britain (1760-1801)

Monarchs of the United Kingdom of Great Britain and Ireland:

George III of the United Kingdom (1801-1820). By the Act of Union of 1800, the previous personal union with the Irish crown was replaced by a political union. The united entity was known as the "United Kingdom of Great Britain and Ireland".
George IV of the United Kingdom (1820-1830)
William IV of the United Kingdom (1830-1837)
Victoria of the United Kingdom (1837-1901)
Edward VII of the United Kingdom (1901-1910)
George V of the United Kingdom (1910-1927)

Monarchs of the United Kingdom and of Ireland:

George V of the United Kingdom (1927-1936)
Edward VIII of the United Kingdom (1936)
George VI of the United Kingdom (1936-1949)

Monarchs of the United Kingdom of Great Britain and Northern Ireland:
George VI of the United Kingdom (1949-1952). Following the declaration of the Republic of Ireland in 1949, only that part of Ireland known as Northern Ireland retained the British monarchy.
Elizabeth II of the United Kingdom (1952-)

Kings George I, II, and III had reigned as "King of Ireland"; after a constitutional change Georges III & IV had reigned as "King of the United Kingdom of Great Britain and Ireland." Edward VIII was the first monarch to accede to the British throne with the Northern Ireland designation attached to his title. His brother, George VI was the first actually so crowned. He was also the last Monarch to reign as King in all of the island of Ireland.