1 - The Brythonic Kings of Strathclyde
Ceretic Guletic is the first recorded ruler of of the kingdom of Strathclyde and the probable founder of the kingdom in the mid to late fifth century whose historicity is well attested.
There are many different versions of king lists for the rulers of Strathclyde, particularly in respect of those between Ceretic Guletic and Riderch; sometimes it seems as if names are just being tossed in willy-nilly from any old source. The above list seems to be the closest to historical truth. It is also common to include the name of Constantine as successor to 'Riderch' or Rhydderch Hael; this is a complete fiction drawn from the later medieval Life of Kentigern.
2 - Post Viking Brythonic kings
After the death of Eochaid map Rhun it is entirely unclear what happened in Strathclyde and in particular what role, if any the Vikings played after they captured the Strathclyde capital of Alt Cluid in 870. The next known rule of the kingdom is one Doneualdus whose death can be reasonably dated to the year 925.
3 - The Sub-Kings under Scottish Rule
In 946 Edward king of England conquered Strathclyde and ceded it to Malcolm I king of Scots. Malcolm I seems to have adopted the practice of appointing his nominated successor as sub-king of Strathclyde, a precedent that was later followed by others as many went on to be the kings of the wider kingdom at a later date.
Opinions differ as to who was the last king of Strathclyde; as after the death of Eoghain the Bald in 1018 it is not absolutely certain that the future Duncan I, the chosen heir of Malcolm II was king of Strathclyde or not. What is certain is that after the death of Duncan the Scots dispensed with the idea of a separate identity for Strathclyde although the distinct Brythonic culture and language survived well into the twelfth century.
Explanatory footnote.
When I originally posted this write up, it was divided into two simple sections
1 - The Brythonic Kings of Strathclyde
2 - The Sub-Kings under Scottish Rule
and under the latter heading I wrote;
After the death of Eochaid map Rhun the kingdom of Strathclyde came under the rule of the kings of the Scots and from 908 onwards they appointed sub-kings to govern Strathclyde
And listed the following three rulers;
Although this is fairly standard history it is also entirely wrong. It is based on a mis-reading of The Chronicle of the Kings of Alba by a fourteenth century historian by the name of John of Fordun who mistook a reference to the deaths of Doneualdus king of the Britons and Duneualdus son of Ede in the same year as a reference to the Scottish Donald mac Aed when in fact it refers to an entirely different Irish king Domnall mac Aede and an entirely different Dyfnwal/Donald king of Strathclyde.
Which also means that the Owain/Owen/Eochaid/Eoghain that ruled Strathclyde at the time of the battle of Brunaburh was therefore not the son of Donald mac Aed.
This information was derived from
http://sbaldw.home.mindspring.com/hproject/prov/donal000.htm which quotes it source as;
B. T. Hudson, Elech and the Scots in Strathclyde, Scottish Gaelic Studies 15 (1988), 145-9
Having read the entry (Chapter 28) in the The Chronicle of the Kings of Alba it can quite clearly be seen that the Strathclyde Doneualdus is not the same person as the Scottish Donald mac Aed.