I might have worded the question wrong, I was referring to the earliest coins minted on the British Isles (the land mass) by Kings or Chieftains that ruled there. Also the earliest KNOWN ruler.
Now the story of Commios, as I understand it, is that he might have been from the continent, drafted by Caesar to go to Britain and prepare them to be taken. Caesar thought that he, being the same in the eyes of a Roman as the 'barbarians' in Britain, might persuade them to give up without a fight or some such thing. It is obvious by the coins found that he set himself up as a local ruler, or had already done so as he was able to gather troops from his tribe that seems to have been in Britain according to accounts. If nothing else, his successors were obviously rulers in Britain and also minted coinage identifying themselves.
I THINK that makes HIM the oldest known ruler (not king of all Briton but A king or chieftain in Briton, one of many) to mint a coin that can be traced to him. I was just assuming that if he was the first to identify himself on a COIN. Then maybe others might have identified themselves some other way, or their existence can be verified in other ways.
I started wondering this after reading the Historia Regum Britanniae written in 1136 by Geoffrey of Monmouth. It chronicles the lives of the kings of the Britons spanning a time of two thousand years, beginning with the Trojans of Homer's Iliad up until the Anglo-Saxons. Now I know this has little to no real historical value but all the same, apparently many of the names seem to have been real kings mentioned in lists of old rulers. Many of the names used ARE mentioned in the histories of other nations such as Brennus who captured Rome in 390 BC. Probably a Gaul borrowed for the story but still a figure known to history to have existed. It seems the history does pull in names of real early kings that might have existed or who are mentioned in other ancient sources.
So as I looked around I found Varimundus, the Kings of Mercia and the Kings of Northhumbria whose coins were VERY interesting. I love the early Anglo Saxon coins but found that coins had been minted long before them by what would, I assume, generally be called the Celts. They have coins that date back well before the invasion by Caesar but none identified who was minting them before Commios...and he was probably influenced by the Roman Denarius.
So it just got me to wondering if I was missing something, if the list goes further back and other early kings can be identified by other means besides a coin inscription and if Commios WAS the earliest identifiable ruler.
Anyway, some of the post roman occupation coins are simply outstanding. Interesting designs, often very attractive in their simplicity. Here is coin I found while looking around that I thought was stunning and simple:


Early Anglo Saxon Secondary silver sceat [c.710-60]
'WODAN' HEAD - Type 30b
obv. Wodan head facing with beard, crosses each side
rev. 2 standing figures with cross in between, 2 pellets above and 6 below,
cross at each side
[see Metcalf 430, N.171, S.844, Abramson P940]
few others I found to be very interesting:




Offa^^
What do you think about the Offa coin with arabic writing on it? How did that happen?