Beli I was a ruler of Alt Clut, a Brittonic kingdom based on Dumbarton Rock, some time in the 7th century.
The Harleian genealogies name Beli as the son of Neithon, his predecessor as king, and the father of Eugein I, his successor.
[1] Beli map Neithon is probably identifiable as the Beli who was the father of Bridei III of the Picts, as the Elegy for Bruide mac Bili attributed to Adomnán calls Bridei mac rígh Ala Cluaithe ("son of the King of Alt Clut").
[2] The Annales Cambriae entry for 627 refers to the death of a certain Belin, who may be identified with Beli map Neithon.
[2][5] 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.