Isaac of Dalmatia was a Christian monk and abbot who lived during the fourth century. Originally a hermit residing in the wilderness near Constantinople, he gained prominence for confronting the Emperor Valens regarding the persecution of Nicene Christians. Following the emperor's death, Isaac became the first leader of a monastery established for him in the imperial city. He is recognized as a confessor and a defender of orthodoxy, specifically through his involvement in the Second Ecumenical Council held in 381.