Joannicius the Great was an 8th-century Byzantine monk and theologian who lived as a hermit on Mysian Olympus. After serving in the imperial army, where he reportedly saved a leader during the Battle of Marcellae, he transitioned to a life of monastic contemplation. He is primarily remembered for his intense asceticism and his steadfast defense of icon veneration during a period of iconoclasm in the Byzantine Empire. His life and spiritual influence are documented through hagiographical accounts that detail his devotion to prayer and the Psalms.