King of Wales was a very rarely used title, because Wales never achieved the degree of political unity that England or Scotland did. However, in the mid-11th century, one of the Welsh kings, Gruffydd ap Llywelyn, gained supreme power: "in 1055 he absorbed Deheubarth (i.e., southern Wales) as well, thus becoming in effect King of Wales"[1]. Historian John Davies 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."[2]

Gruffydd ap Llywelyn was, however, not referred to as King of Wales at the time, but rather as King of the Britons. 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 bestowed upon two subsequent Welsh Kings of the 12th century: Gruffudd ap Cynan (probably retrospectively) and his son Owain Gwynedd. "In his first two letters to Louis, Owain described himself as 'king of Wales' and 'king of the Welsh'"[3] Their direct rule was however limited to Gwynedd. After the death of Owain Gwynedd in 1170, the mantle of paramount Welsh ruler was taken up by Rhys ap Gruffydd, who was called Head of all Wales by the Brut y Tywysogion 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), see King of the Britons.