Iserninus was a 5th-century Christian missionary and bishop who played a role in spreading the faith across southern Ireland. Traditionally, he is linked to the work of Saint Patrick and Saint Auxilius, though contemporary scholars often connect him instead to Palladius. Originally named Fith, he may have been ordained as a deacon in Auxerre. His missionary activities are recorded as beginning around 439 AD, and he is frequently associated with the territories of the Uí Cheinnselaig in Leinster.