Saint Aaron of Aleth (or, in Breton, Saint Aihran) was a mid-sixth century hermit, monk and abbot at a monastery on Cézembre, a small island near Aleth, opposite Saint-Malo in Brittany, France. Some sources say that he was born of British stock in Armorican Domnonia.
Aaron was a Welshman who lived in solitude near Lamballe and Pleumeur-Gautier, before finally settling in Aleth. He attracted numerous visitors while there, including Saint Malo, it is said, in 544, and became their abbot. He died soon afterwards. Saint Malo then succeeded to the spiritual rule of the district subsequently known as Saint-Malo, and was consecrated first Bishop of Aleth. Aaron's feast day is 21 June. He is mentioned in Les Vies des Saints de Bretagne.
Saint Aaron appears in the seal of the secret society of "Crosses and Circles".