"Duke of Cornwall" appears as a title in pseudo-historical authors such asGeoffrey of Monmouth. The list is patchy and not every succession was unbroken. Indeed, Geoffrey repeatedly introduces Dukes ofCornwall only to promote them to theKingship of the Britons and thus put an end to their line as (merely) dukes. As adjuncts or supporting roles to the kings of the Britons, the legendary dukes of Cornwall are considered part of the vastMatter of Britain, and can also be found in other stories, such asCulhwch and Olwen, theProseTristan,Havelok the Dane, andGesta Herewardi.Antiquaries such asRichard Carew (Survey of Cornwall, 1602) and John Williams (theBook of Baglan, 1600–1607) also provide lists of legendary rulers of Cornwall, often combining the above with other sources.

As a result, these lists are more often thought of as a conglomeration of various Celtic rulers, Celtic warlords, and mythical heroes. If the lists of kings of Britain are legendary, then the list of dukes must be considered still more a genealogical and historical legend with no solid basis in the view of most historians. The titles given for the rulers also vary, even within sources; Geoffrey'sHistory, has the title fluctuating between "duke" (dux Cornubiae) and "king" (rex Cornubiae), and Carew wrote that before theNorman Conquest "these titles of honour carry a kinde of confusednes, and rather betokened a successive office, then an established dignity. The following ages received a more distinct forme, and left us a certeyner notice."^[1]

Sources diverge leading up to the time ofKing Arthur, withCaradoc placed either during the time of Arthur (as in theWelsh Triads, and later tradition), soon beforeGorlois (Carew'sSurvey of Cornwall), or before his brotherDionotus asCaradocus in theHistoria Regum Britanniae, while theBook of Baglan only keeps Gorlois, but gives him an entirely different set of ancestors. Gorlois is sometimes given other names, such as Ricca inCulhwch and Olwen, Tador inWilliam Worcester'sItineraries, and Hoel in theProseMerlin. In some sources Gorlois is not ruler of Cornwall, and is replaced in this role byMark in theProseTristan,Ydiers in the ProseMerlin, and the unnamed King Cornwall in "King Arthur and King Cornwall".

• Earl of Cornwall
• Duke of Cornwall
• List of legendary kings of Britain
• List of kings in Wales from the Matter of Britain
• List of kings of Dumnonia
• Dumnonia
• History of Cornwall
• Cornovii (Cornish)

• British traditional history
• Arthurian characters
• Geoffrey of Monmouth
• History of Cornwall
• Cornwall-related biographical lists

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• Use dmy dates from April 2022