King of Wales was a very rarely used title, because Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

 never achieved the degree of political unity that England

Kingdom of England

The Kingdom of England was, from 927 to 1707, a sovereign state to the northwest of continental Europe. At its height, the Kingdom of England spanned the southern two-thirds of the island of Great Britain and several smaller outlying islands; what today comprises the legal jurisdiction of England...

 or Scotland

Kingdom of Scotland

The Kingdom of Scotland was a Sovereign state in North-West Europe that existed from 843 until 1707. It occupied the northern third of the island of Great Britain and shared a land border to the south with the Kingdom of England...

 did. However, in the mid-11th century, one of the Welsh kings, Gruffydd ap Llywelyn

Gruffydd ap Llywelyn

Gruffydd ap Llywelyn was the ruler of all Wales from 1055 until his death, the only Welsh monarch able to make this boast...

, gained supreme power: "in 1055 he absorbed Deheubarth (i.e., southern Wales) as well, thus becoming in effect King of Wales". Historian John Davies

John Davies (historian)

John Davies is a Welsh historian, and a television and radio broadcaster.Davies was born in the Rhondda, Wales, and studied at both University College, Cardiff, and Trinity College, Cambridge. He is married with four children...

 states that Gruffydd was "the only Welsh king ever to rule over the entire territory of Wales... Thus, from about 1057 until his death in 1063, the whole of Wales recognised the kingship of Gruffudd ap Llywelyn. For about seven brief years, Wales was one, under one ruler, a feat with neither precedent nor successor."

Gruffydd ap Llywelyn was, however, not referred to as King of Wales at the time, but rather as "King of the Britons

King of the Britons

The Britons or Brythons were the Celtic-speaking people of what is now England, Wales and southern Scotland, whose ethnic identity is today maintained by the Welsh, Cornish and Bretons...

". He was the last of a long line of paramount rulers among the insular Britons to have this title bestowed upon him, and possibly the only one to truly rule over all the (independent) Britons. For by this time, if not earlier, Wales was the only part of Britain remaining under Brittonic rule.

The title King of Wales was used by at least one later Welsh ruler, Owain Gwynedd

Owain Gwynedd

Owain Gwynedd ap Gruffydd , in English also known as Owen the Great, was King of Gwynedd from 1137 until his death in 1170. He is occasionally referred to as "Owain I of Gwynedd"; and as "Owain I of Wales" on account of his claim to be King of Wales. He is considered to be the most successful of...

. "In his first two letters to Louis, Owain described himself as 'king of Wales' and 'king of the Welsh'" His direct rule was however limited to Gwynedd

Kingdom of Gwynedd

Gwynedd was one petty kingdom of several Welsh successor states which emerged in 5th-century post-Roman Britain in the Early Middle Ages, and later evolved into a principality during the High Middle Ages. It was based on the former Brythonic tribal lands of the Ordovices, Gangani, and the...

. After the death of Owain Gwynedd

Owain Gwynedd

Owain Gwynedd ap Gruffydd , in English also known as Owen the Great, was King of Gwynedd from 1137 until his death in 1170. He is occasionally referred to as "Owain I of Gwynedd"; and as "Owain I of Wales" on account of his claim to be King of Wales. He is considered to be the most successful of...

 in 1170, the mantle of paramount Welsh ruler was taken up by Rhys ap Gruffydd

Rhys ap Gruffydd

Rhys ap Gruffydd or ap Gruffudd was the ruler of the kingdom of Deheubarth in south Wales. He is commonly known as The Lord Rhys, in Welsh Yr Arglwydd Rhys, but this title may not have been used in his lifetime...

, who was called "Head of all Wales" by the Brut y Tywysogion

Brut y Tywysogion

Brut y Tywysogion is one of the most important primary sources for Welsh history. It is an annalistic chronicle that serves as a continuation of Geoffrey of Monmouth’s Historia Regum Britanniae. Brut y Tywysogion has survived as several Welsh translations of an original Latin version, which has...

 on his death in 1197. His direct rule was limited to Deheubarth. For a list of Welsh rulers upon whom titles such as these were bestowed (leading ultimately to the title Prince of Wales

Prince of Wales

Prince of Wales is a title traditionally granted to the heir apparent to the reigning monarch of the United Kingdom of Great Britain and Northern Ireland and the 15 other independent Commonwealth realms...

), see King of the Britons

King of the Britons

The Britons or Brythons were the Celtic-speaking people of what is now England, Wales and southern Scotland, whose ethnic identity is today maintained by the Welsh, Cornish and Bretons...

.