Which of these was known in medieval British history as the founder and first king of Britain?

Just plain wrong, the Roman's invaded Britain, they didn't name or invent it!

Fake as King Arthur being Roman. Attack on identity. England = Land of Angles. Britain is Celtic = painted ones (blue woad). It's what others called the inhabitants. Same as Wales is a Germanic term for foreigner but really it's Cymru (cym means valley).

luckycatfay, The kingdoms you mentioned, along with others such as Kent, Essex, Bernicia, North umbria, etc. are all Anglo-Saxon kingdoms which date from the 5th century i.e. post the Roman withdrawal from Britain.

luckycatfay, Medieval historians where not aware of the origins of the country as there is no written evidence detailing this, so therefore took what information they had from the Classicial literature available and made it fit. The general believe for most societies was that there was a single founder. You are correct in saying that Britain was divided into smaller kingdoms, but this was the case both before and after the Roman conquest of AD 43/44.

Never heard this before & I've studied history of Britain. Plus I live here 🤔

Never heard of this don't think it's right Britain was ruled by small areas split between places like wessex mercia until the roman invasion and that guy was never mentioned.