This may refer to Mahon (Mathgamain mac Cennétig), a southern chieftain and the elder brother of Brian Boru, who is believed by some to have fought a battle in 960 in the vicinity of Ballymahon at Shrule (in Irish "Sruaith Fhuil", River of Blood) where he defeated O'Rourke of Cavan and laid claim to lands in the area.