Conomor (fl. c. 540), also known as Conomerus or Conomor the Cursed, was an early medieval ruler of Brittany. His name, which has the Welsh cognate Cynfawr, means "Great Dog", but could also indicate "Sea Dog" in early Brythonic. Conomor was notorious for his cruelty, becoming a legendary villain in Breton culture. He is widely regarded as one of the probable sources for the myth of Bluebeard and possibly also of Tristan's uncle King Mark of Cornwall. The wife-beating giant Cormoran may also retain a garbled folk memory of the same character.
Conomor was king of Domnonée, and Prince of Poher; Domnonée was, at this time, expanding to claim control over all Brythonic territory in Armorica (Brittany). It is difficult to disentangle the Conomor of legend from the historical ruler. As with other early Breton rulers most written information about him comes from the lives of Breton saints.
The name Conomor is mentioned in Cornish genealogies, and may have established himself in Brittany after a youth in Cornwall, i.e. Dumnonia. He is mentioned in the Historia Francorum by Gregory of Tours as a mid-6th century Breton count involved in conflicts between the Breton count Chanao and his brother Macliau (in latin, Macliavus). According to Gregory, after Chanao killed his other brothers, Macliau fled to Conomor. Conomor "hid him in a box underground" which he claimed was Macliau's grave. When Chanao was satisfied he was dead, Macliau was secretly placed in a monastery. After Chanao's death he returned to take over his brother's realm.
Conomor is listed as "prefectus du roi des Francs" in the life of Saint Tugdual and in the life of Saint Paul Aurelian he is called ruler of "different peoples of four languages", which may suggest that his territory included both Brittany and Cornwall. Conomor is said to have been count of Carhaix and to have become king by murdering his predecessor Jonas. He married Jonas' widow, but she later fled from him to seek asylum in the Frankish court with her son Judael. He is later said to have come into conflict with Waroch II, count of Vannes, whose daughter Tréphine he had married after his first wife's death. In unclear circumstances he is said to have murdered Tréphine and later his son by her, Trémeur. Eventually the local bishops were persuaded by Saint Samson to excommunicate Conomor. It is possible that the story of Tréphine and Trémeur is a garbled version of Conomor's attempts to kill Judael, his step-son. According to Lester K. Little, "Conomor was serving as regent for a nephew who was too young to take up the kingship he had inherited; the main grievance against him was his relentless campaign to have the boy killed. Those present in the assembly ineluded Saint Hervé the blind poet and perhaps also Saint Samson of Dol, Saint Gildas, and Saint Teilo of Glamorgan. Against Conomor all those assembled launched an excommunication."