Salomon (Breton: Salaün) (died 874) was Count of Rennes and Nantes from 852 and Duke of Brittany from 857 until his death by assassination. He used the title King of Brittany intermittently after 868. In 867, he was granted the counties of Avranches and Coutances.
In popular tradition within Brittany he was canonised as "Saint Salomon" after his death and raised to the rank of martyr.
Salomon was the son of Riwallon III of Poher. In 851, Charles the Bald, after his defeat at the Battle of Jengland, made peace with Erispoe, the Breton duke, and granted him the counties of Rennes and Nantes and the Pays de Retz in Poitou as far as the river Mayenne. In 852, Salomon swore an oath to Charles and became his loyal follower (fidelis); in return, in a manner similar to Erispoe, he was granted Rennes, Nantes, and Retz as a "third" of Brittany to be held from Charles in fee. He and Erispoe were the dominatores of Rennes in 853. Salomon was the most powerful aristocrat at Erispoe's court.
Probably because he feared losing his benefices (which he held under Erispoe) if Louis the Stammerer were allowed to become king at Le Mans, Salomon colluded with the otherwise unknown Almarchus to assassinate his cousin Erispoe and seize the Breton throne in 857. In 858, he was behind the large-scale revolt of the Frankish nobles of Neustria against Charles the Bald. Bretons were involved in the chasing of Louis from Le Mans in Spring that year. In September, Louis the German marched as far as Orléans, where a Breton delegation from Salomon met him and took oaths on Salomon's behalf. In 859, a synod met at Savonnières near Toul and tried to order Salomon to remember his oath of 852 and to resume paying the tribute which Brittany had paid in years past.