King of the Britons in the context of List of rulers of Brittany

Leir was a legendary king of the Britons whose story was recounted by Geoffrey of Monmouth in his pseudohistorical 12th-century History of the Kings of Britain. According to Geoffrey's genealogy of the British dynasty, Leir reigned around the 8th century BC, around the time of the founding of Rome. The story was modified and retold by William Shakespeare in his Jacobean tragedy King Lear.

This is a list of rulers of Brittany. In different epochs the rulers of Brittany were kings, princes, and dukes. The Breton ruler was sometimes elected, sometimes attained the position by conquest or intrigue, or by hereditary right. Hereditary dukes were sometimes a female ruler, carrying the title duchesse of Brittany. Its principal cities and regions were ruled by counts who often found themselves in conflict with the Breton ruler, or who became the Breton ruler.

During the declining years of the Roman Empire, the earliest Breton rulers in Gaul were styled "kings" of the small realms of Cornouaille and Domnonée. Some such kings may have had a form of hegemony over all of the Brythonic populations in the Armorican peninsula, and Riothamus is called King of the Britons by the chronicler Jordanes. However, there are no certain rulers of the whole of Brittany, which was divided into the fiefdoms of local counts.

Cadwallon ap Cadfan (died 634) was the King of Gwynedd from around 625 until his death in battle. The son and successor of Cadfan ap Iago, he is best remembered as the King of the Britons who invaded and conquered Northumbria, defeating and killing its king, Edwin, prior to his own death in battle against Oswald of Bernicia. His conquest of Northumbria, which he held for a year or two after Edwin died, made him one of the last recorded Celtic Britons to hold substantial territory in eastern Britain until the rise of the Welsh House of Tudor. He was thereafter remembered as a national hero by the Britons and as a tyrant by the Anglo-Saxons of Northumbria. Uniquely among seventh-century Welsh monarchs, Cadwallon also has three poems associated with him, which may be contemporaneous to his lifetime.

This is a list of the rulers of the Kingdom of Gwynedd. Many of them were also acclaimed "King of the Britons" or "Prince of Wales".

Hywel ap Cadell, commonly known as Hywel Dda, which translates to Howel the Good in English, was a Welsh king who ruled the southern Welsh kingdom of Deheubarth and eventually came to rule most of Wales. He became the sole king of Seisyllwg in 920 and shortly thereafter established Deheubarth, and proceeded to gain control over the entire country from Prestatyn to Pembroke. As a grandson of Rhodri Mawr through his father Cadell, Hywel was a member of the Dinefwr branch of the dynasty. He was recorded as King of the Britons in the Annales Cambriæ and the Annals of Ulster.

Hywel is highly esteemed among other medieval Welsh rulers. His name is particularly linked with the codification of traditional Welsh law, which were thenceforth known as the Laws of Hywel Dda. The latter part of his name (Dda, lit. "Good") refers to the fact that his laws were just and good. The historian Dafydd Jenkins sees in them compassion rather than punishment, plenty of common sense and recognition of the rights of women. Hywel Dda was a well-educated man even by modern standards, having a good knowledge of Welsh, Latin and English.

The Kingdom of Gwynedd was a Welsh kingdom which first appeared at the turn of the sixth century. Based in northwest Wales, the rulers of Gwynedd repeatedly rose to dominance and were acclaimed as "King of the Britons" before losing their power in civil wars or invasions. The kingdom of Gruffudd ap Llywelyn—the King of Wales from 1055 to 1063—was shattered by a Saxon invasion in 1063 just prior to the Norman invasion of Wales, but the House of Aberffraw restored by Gruffudd ap Cynan slowly recovered and Llywelyn the Great of Gwynedd was able to proclaim the Principality of Wales at the Aberdyfi gathering of Welsh princes in 1216. In 1277, the Treaty of Aberconwy between Edward I of England and Llywelyn's grandson Llywelyn ap Gruffudd granted peace between the two but would also guarantee that Welsh self-rule would end upon Llywelyn's death, and so it represented the completion of the first stage of the conquest of Wales by Edward I.

Welsh tradition credited the founding of Gwynedd to the Brittonic polity of Gododdin (Old Welsh Guotodin, earlier Brittonic form Votadini) from Lothian invading the lands of the Brittonic polities of the Deceangli, Ordovices, and Gangani in the 5th century. The sons of their leader, Cunedda, were said to have possessed the land between the rivers Dee and Teifi. The true borders of the realm varied over time, but Gwynedd proper was generally thought to comprise the cantrefs of Aberffraw, Cemais, and Cantref Rhosyr on Anglesey and Arllechwedd, Arfon, Dunoding, Dyffryn Clwyd, Llŷn, Rhos, Rhufoniog, and Tegeingl at the mountainous mainland region of Snowdonia opposite.

Cassivellaunus was a historical British military leader who led the defence against Julius Caesar's second expedition to Britain in 54 BC. He led an alliance of tribes against Roman forces, but eventually surrendered after his location was revealed to Julius Caesar by defeated Britons.

Cassivellaunus made an impact on the British consciousness. He appears in British legend as Cassibelanus, one of Geoffrey of Monmouth's kings of the Britons, and in the Mabinogi, Brut y Brenhinedd and the Welsh Triads as Caswallawn, son of Beli Mawr.

Cunobeline or Cunobelin (Common Brittonic: *Cunobelinos, "Dog-Strong"), also known by his name's Latin form Cunobelinus, was a king in pre-Roman Britain from about AD 9 to about AD 40. He is mentioned in passing by the classical historians Suetonius and Dio Cassius, and many coins bearing his inscription have been found. He controlled a substantial portion of southeastern Britain, including the territories of the Catuvellauni and the Trinovantes, and he was called "King of the Britons" (Britannorum rex) by Suetonius. Cunobeline may have been a client king of Rome, based on the images and legends appearing on his coins. Cunobeline appears in British legend as Cynfelyn (Welsh), Kymbelinus (medieval Latin) or Cymbeline, as in the play by William Shakespeare.

Idwal Foel (Idwal the Bald) (died c. 942) or Idwal ab Anarawd (Idwal son of Anarawd) was a 10th-century King of Gwynedd in Wales. A member of the House of Aberffraw, he inherited the throne from his father, Anarawd ap Rhodri. William of Malmesbury credited him as "King of the Britons" in the manner of his father.