The kings of Dumnonia were the rulers of the large Brythonic kingdom of Dumnonia in the south-west of Great Britain during the Sub-Roman and early medieval periods. A list of Dumnonian kings is one of the hardest of the major Dark Age kingdoms to accurately compile, as it is confused by Arthurian legend, complicated by strong associations with the kings of Wales and Brittany, and obscured by the Saxon advance. Therefore, this list should be treated with caution.

Dumnonian kings

The original Celtic chiefs of the Dumnonii ruled in the south-west corner of the British Isles until faced with the arrival of the Romans in their territory in c. AD 55, when the Romans established a legionary fortress at Isca Dumnoniorum (modern Exeter). Although subjugated by c. AD 78, the civitas Dumnoniorum was among the regions of Roman Britain least affected by Roman influence. Known as Caer Uisc, Exeter was inhabited by Dumnonian Britons until c. 936, when King Athelstan expelled them. Several other royal residences may also have served the kings of Dumnonia or Cornwall, including Tintagel and Cadbury Castle. see also Domnonée. (The earlier portion follows the Dumnonian line beginning with Gereint, Cado, Erbin, Guitol ap Gradlon, Marchell, and Riothamus )

Native tradition

Susan Pearce views the only native 4th- to 7th-century Dumnonian rulers known to history as: Pearce identifies Constantine with the Constantine mentioned by Gildas, anchoring his reign to the 6th century, and giving later dates for the reigns of Erbin, Geraint, and Cadwy.

Cornish kings

By the end of the 8th century, Dumnonia was much reduced in size by the advance of the West Saxons and the remaining territory became a rump state in Cornwall. An early 17th century pedigree of a so-called 'Earl of Cornwall' in the Book of Baglan may possibly represent a list of rulers in Cornwall.

Cornish earls

If he is not to be identified with Hywel Dda of Deheubarth, the singularly recorded Huwal could have been the last native king. Some of the later supposed rulers listed below are given the title 'Earl of Cornwall'.

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