The title King of the Britons (Latin: Rex Britannorum, Welsh: Brenin y Brythoniaid) was used (often retrospectively) to refer to the most powerful ruler among the Celtic Britons, both before and after the period of Roman Britain up until the Norman conquest of England. The Britons were the Brittonic-speaking peoples of what is now England, Wales, and southern Scotland, whose ethnic identity is today maintained by the Welsh, Cornish and Bretons.
The same title was also used to refer to some of the rulers of Brittany in the ninth century, but there it is best translated as King of the Bretons (Roue an Breizhad). This page concerns only rulers in Britain (with the exception of Riothamus, who may have ruled both in Britain and Continental Europe.)
At least twenty kings were referred to as "King of the Britons", while others were given related titles or descriptions. The table below also contains the paramount native Welsh rulers in the Norman and Plantagenet periods – by this time only Wales (or parts thereof) remained under Brittonic rule in Britain and the term "Britons" (Brythoniaid, Brutaniaid) was used in Britain to mean the Welsh people (Cymry in modern Welsh). This, and the diminishing power of the Welsh rulers relative to the Kings of England, is reflected in the gradual evolution of the titles by which these rulers were known from "King of the Britons" in the 11th century to "Prince of Wales" in the 13th.
Although the majority of the rulers listed below had their power base in Gwynedd in North Wales, most insular Brittonic areas from the 7th century on are to be found in the list below, from Dumnonia in the West Country, to Strathclyde in southwest Scotland.
|Name||Reign||Regional power base||Recorded title or description||Source||Notes|
|Cunobeline||c. 9 – c. 41||lands of the Trinovantes and Catuvellauni||King of the Britons||Suetonius||perhaps retrospective|
|Tiberius Claudius Cogidubnus||mid- to late 1st century||lands of the Regni, Atrebates, and Belgae||Great King of the Britons (or perhaps: Great King of Britain)||marble inscription at Chichester||contemporary, self-description|
|Vortigern||mid-5th century||unknown, but traditionally Powys||King of the Britons (in c. 449)||Bede||probably retrospective|
|Riothamus||c. 469||unknown, but active in Gaul||King of the Britons (in c. 469)||Jordanes||may refer only to Britons in Gaul|
|Ambrosius Aurelianus||late 5th century||probably in the south||Leader [of the Britons]||Gildas||near contemporary|
|unnamed||c. 545||unknown||King over them [the Britons]||Procopius||contemporary but distant|
|Maelgwn Gwynedd||?–549?||Gwynedd||King [who] reigned among the Britons||Historia Brittonum||retrospective|
|Selyf ap Cynan||?–c. 613||Powys||King of the Britons (in c. 613)||Annals of Ulster||near contemporary|
|Ceretic of Elmet||c. 614 – 617||Elmet||King of the Britons (in 614)||Bede||may refer only to Britons in Elmet|
|Cadwallon ap Cadfan||?–634||Gwynedd||(Cadwalla,) King of the Britons (in 633)||Bede|
|Idris||?–635||unknown. perhaps Meirionnydd||King of the Britons (in 635)||Annals of Ulster (sub anno 633)||perhaps Idris Gawr|
|Eugein I of Alt Clut||c. 642||Strathclyde||King of the Britons (in 642)||Annals of Ulster|
|Cadwaladr||c. 654 – c. 664||Gwynedd||[King who] reigned among the Britons||Historia Brittonum||retrospective|
|Geraint||?670–c. 710||Dumnonia||King of the Welsh (=Britons) (in 710)||Anglo-Saxon Chronicle||may refer only to Britons in Dumnonia|
|Rhodri Molwynog||c. 712 – 754||Gwynedd||King of the Britons (in 754)||Annales Cambriae||perhaps retrospective|
|Cynan Dindaethwy||798–816||Gwynedd (insecurely from 754)||King of the Britons (in 816); The King (in 816)||Annals of Ulster; Annales Cambriae|
|Merfyn Frych||825–844||Gwynedd||King of the Britons (in 829); Glorious King of the Britons||Historia Brittonum; Bamberg Cryptogram||contemporary|
|Rhodri the Great||844–878||Gwynedd, from 855 also Powys, from 872 also Seisyllwg||King of the Britons (in 878)||Annals of Ulster|
|Anarawd ap Rhodri||878–916||Gwynedd||King of the Britons (in 916)||Annales Cambriae|
|Idwal Foel ap Anarawd||916–942||Gwynedd||King of the Britons (in 927)||William of Malmesbury|
|Hywel Dda||942–950||Deheubarth (from 920), from 942 also Gwynedd and Powys||King of the Britons (in 950)||Annals of Ulster and Annales Cambriae|
|Dyfnwal ab Owain||930s–970s||Strathclyde||King of the Britons (in 973)||Annals of Ulster|
|Maredudd ab Owain||986–999||Deheubarth and Gwynedd and Powys||King of the Britons (in 999)||Brut y Tywysogion|
|Llywelyn ap Seisyll||1018–1023||Gwynedd and Powys; from 1022 also Deheubarth||King of the Britons (in 1023)||Annals of Ulster|
|Iago ab Idwal||1023–1039||Gwynedd and Powys||King of the Britons (in 1039)||Annals of Ulster|
|Gruffydd ap Llywelyn||1039–1063||Gwynedd and Powys, from 1057 also the rest of Wales||King of the Britons (in 1063; in 1058)||Annals of Ulster; Brut y Tywysogion|
|Bleddyn ap Cynfyn||1063–1075||Gwynedd and Powys and Seisyllwg||Support[er of] the whole Kingdom of the Britons (in 1075); Chiefest of the Britons||Brut y Tywysogion (sub anno 1173; sub anno 1113)|
|Rhys ap Tewdwr||1079–1093||Deheubarth (insecurely until 1081)||[Upholder of the] Kingdom of the Britons (in 1093)||Brut y Tywysogion|
|Gruffudd ap Cynan||1136–1137||Gwynedd (insecurely from 1081)||King of all the Welsh (in 1137)||Brut y Tywysogion|
|Owain Gwynedd||1137–1170||Gwynedd||Prince over the British nation (in 1146); King of Wales, King of the Welsh, Prince of the Welsh||Brut y Tywysogion; contemporary charters|
|Rhys ap Gruffydd||1171–1197||Deheubarth (from 1155)||Head of all Wales (in 1197); Prince of the Welsh (in 1184), Prince of Wales||Brut y Tywysogion; contemporary charters|
|Llywelyn the Great||1208–1240||Gwynedd (from 1194), from 1208 also Powys, from 1216 also Deheubarth||Prince of the Welsh (in 1228); Prince of Wales (in 1240)||Brut y Tywysogion; contemporary charters||probably retrospective;|
|Dafydd ap Llywelyn||1240–1246||Gwynedd||Prince of Wales (from 1220)||treaty with England|
|Llywelyn ap Gruffudd||1258–1282||Gwynedd (from 1246), at times also Powys and Deheubarth||Prince of Wales (in 1264; in 1258; in 1267; 1258–82)||Brut y Tywysogion; treaty with Scotland; treaty with England; letters, charters etc.|
|Dafydd ap Gruffydd||1282–1283||Gwynedd||Prince of Wales (in 1283)||letters|
|Madog ap Llywelyn||1294–1295||Gwynedd||Prince of Wales (in 1294)||Penmachno Document|
|Interregnum (English rule)|
|Owain Glyndŵr||1400 – c. 1410||Northern Powys, by 1404–5 all Wales, by 1409 only Gwynedd||Prince of Wales (from 1400)||contemporary records e.g. coronation ceremony (1404)|
- Stuart Laycock (2008). Britannia: The Failed State. Tempus. ISBN 0-7524-4614-2.
- Kari Maund (2000). The Welsh Kings: The Medieval Rulers of Wales. Tempus. ISBN 0-7524-2321-5.
- C. A. Snyder (2003). The Britons. Blackwell. ISBN 0-631-22260-X.
- Procopius (2000). History of the Wars (book 8, chapter 20, verses 6–10). Translated by H. B. Dewing. Harvard University Press. ISBN 0-674-99191-5.
- Annals of Ulster, 633.1 "Bellum Iudris regis Britonum"
- Carpenter, David (2003). The struggle for mastery: Britain 1066–1284.
- Pierce, Thomas Jones. "Dafydd (David) ap Gruffydd". Welsh Biography Online. The Honourable Society of Cymmrodorion. Retrieved 5 April 2011.