Diomedes of Tarsus was a Greek physician and Christian evangelist who lived during the late third and early fourth centuries. Born in Tarsus, he traveled extensively to spread his faith. While traveling toward Nicomedia following his arrest by order of Diocletian, he stopped to pray and subsequently died. His death occurred in or near Nicaea (modern-day İznik). He is recognized as a martyr and is honored among the group of saints known as the Holy Unmercenaries.