Selyf ap Cynan (died 616) appears in Old Welsh

Old Welsh language

Old Welsh is the label attached to the Welsh language from about 800 AD until the early 12th century when it developed into Middle Welsh. The preceding period, from the time Welsh became distinct from the British language around 550, has been called "Primitive Welsh".Many poems and some prose...

 genealogies as an early 7th century King of Powys, the son of Cynan Garwyn

Cynan Garwyn

Cynan Garwyn was king of Powys in the north-east and east of Wales, who flourished in the second half of the 6th century. Little reliable information exists which can be used to reconstruct the background and career of the historical figure...

.

His name is a Welsh

Welsh language

Welsh is a member of the Brythonic branch of the Celtic languages spoken natively in Wales, by some along the Welsh border in England, and in Y Wladfa...

 form of Solomon

Solomon

Solomon , according to the Book of Kings and the Book of Chronicles, a King of Israel and according to the Talmud one of the 48 prophets, is identified as the son of David, also called Jedidiah in 2 Samuel 12:25, and is described as the third king of the United Monarchy, and the final king before...

, appearing in the oldest genealogies as Selim. He reputedly bore the nickname Sarffgadau, meaning battle-serpent. According to the Annals of Ulster

Annals of Ulster

The Annals of Ulster are annals of medieval Ireland. The entries span the years between AD 431 to AD 1540. The entries up to AD 1489 were compiled in the late 15th century by the scribe Ruaidhrí Ó Luinín, under his patron Cathal Óg Mac Maghnusa on the island of Belle Isle on Lough Erne in the...

 and the Annals of Wales, in 616 he died at the Battle of Chester

Battle of Chester

The Battle of Chester was a major victory for the Anglo Saxons over the native Britons near the city of Chester, England in the early 7th century. Æthelfrith of Northumbria annihilated a combined force from the Welsh kingdoms of Powys, Rhôs and possibly Mercia...

, fighting against Æthelfrith of Northumbria

Æthelfrith of Northumbria

Æthelfrith was King of Bernicia from c. 593 until c. 616; he was also, beginning c. 604, the first Bernician king to also rule Deira, to the south of Bernicia. Since Deira and Bernicia were the two basic components of what would later be defined as Northumbria, Æthelfrith can be considered, in...

. The Annals of Ulster

Annals of Ulster

The Annals of Ulster are annals of medieval Ireland. The entries span the years between AD 431 to AD 1540. The entries up to AD 1489 were compiled in the late 15th century by the scribe Ruaidhrí Ó Luinín, under his patron Cathal Óg Mac Maghnusa on the island of Belle Isle on Lough Erne in the...

 entitle him 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...

, perhaps because he led a combined force from more than one Brythonic

Britons (historical)

The Britons were the Celtic people culturally dominating Great Britain from the Iron Age through the Early Middle Ages. They spoke the Insular Celtic language known as British or Brythonic...

 kingdom at that battle against the Northumbrians (the king of 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...

, Iago ap Beli

Iago ap Beli

Iago ap Beli was King of Gwynedd . Little is known of him or his kingdom from this early era, with only a few anecdotal mentions of him in historical documents....

, also died there according to the Annals of Wales).