Beli I was a ruler of Alt Clut

Kingdom of Strathclyde

Strathclyde , originally Brythonic Ystrad Clud, was one of the early medieval kingdoms of the celtic people called the Britons in the Hen Ogledd, the Brythonic-speaking parts of what is now southern Scotland and northern England. The kingdom developed during the post-Roman period...

 (modern Dumbarton Rock), the 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 later known as Strathclyde, some time in the 7th century. Very little is known of him, but his family appears to have been very well connected in northern Britain.

The Harleian genealogies

Harleian genealogies

The Harleian genealogies are a collection of Old Welsh genealogies preserved in British Library, Harleian MS 3859. Part of the Harleian Collection, the manuscript, which also contains the Annales Cambriae and a version of the Historia Brittonum, has been dated to c. 1100, although a date of c.1200...

 name Beli as the son of Neithon

Neithon of Alt Clut

Neithon was a 7th-century ruler of Alt Clut, the Brittonic kingdom later known as Strathclyde . According to the Harleian genealogies, he was the son of Guipno map Dumnagual Hen. Alfred Smyth suggests he is the same man as King Nechtan the Great of the Picts, and perhaps the Nechtan son of Canu...

, his predecessor as king, and the father of Eugein I

Eugein I of Alt Clut

Eugein I was a ruler of Alt Clut , the kingdom later known as Strathclyde, sometime in the mid-7th century. According to the Harleian genealogies, he was the son of Beli I, presumably his predecessor as king, and the father of Elfin, who ruled sometime later...

, his successor. Beli map Neithon is probably identifiable as the Beli who was the father of Bridei III of the Picts

Bridei III of the Picts

King Bridei III was king of Fortriu and overking of the Picts between 671 and his death in 693....

, as the Elegy for Bruide mac Bili attributed to Adomnán calls Bridei mac rígh Ala Cluaithe ("son of the King of Alt Clut"). The Historia Brittonum says that Bridei was the fratruelis or maternal first cousin of Ecgfrith of Northumbria

Ecgfrith of Northumbria

King Ecgfrith was the King of Northumbria from 670 until his death. He ruled over Northumbria when it was at the height of its power, but his reign ended with a disastrous defeat in which he lost his life.-Early life:...

, indicating that Beli's wife might have been of the Northumbria

Northumbria

Northumbria was a medieval kingdom of the Angles, in what is now Northern England and South-East Scotland, becoming subsequently an earldom in a united Anglo-Saxon kingdom of England. The name reflects the approximate southern limit to the kingdom's territory, the Humber Estuary.Northumbria was...

n nobility, though Bridei must have had some Pictish

Picts

The Picts were a group of Late Iron Age and Early Mediaeval people living in what is now eastern and northern Scotland. There is an association with the distribution of brochs, place names beginning 'Pit-', for instance Pitlochry, and Pictish stones. They are recorded from before the Roman conquest...

 connection to become king of Fortriu

Fortriu

Fortriu or the Kingdom of Fortriu is the name given by historians for an ancient Pictish kingdom, and often used synonymously with Pictland in general...

. The Annales Cambriae

Annales Cambriae

Annales Cambriae, or The Annals of Wales, is the name given to a complex of Cambro-Latin chronicles deriving ultimately from a text compiled from diverse sources at St David's in Dyfed, Wales, not later than the 10th century...

entry for 627 refers to the death of a certain Belin, who may be identified with Beli map Neithon. He was certainly dead by 642, the year Irish sources record King Oan or Hoan of Alt Clut (apparently Beli's son Eugein) fighting the Battle of Strathcarron.