He was born in Bithynia of peasant stock. He worked as a swineherd, then became an officer in the Imperial army, where he served with such distinction in the war against the Bulgars that the Emperor Constantine VI wanted to take him into his personal service. "But the sight of massacres and horrors of war had brought home to him the vanity of this life. He asked leave of the Emperor to retire from the service, in order to wage unseen warfare in the ranks of the angelic army" (Synaxarion). In the coming years he traveled widely, sometimes living as a hermit, sometimes living in monasteries, more than once founding a monastic community. Wherever he went he lived in stillness, solitude and strict asceticism. He was famed for his spiritual counsel, his prophecies, his many miracles of healing ailments bodily and spiritual, and for his friendship with animals. Once a monk who doubted the Saint's miracles was eating at table with him when a large bear burst in upon them. Joannicius called the bear and it came and lay at his feet; he then told it to lie at the feet of his frightened guest and said "At their creation, the animals looked with veneration on man, who is made in the image of God, and he had no fear of them. We are afraid of them now because we have transgressed God's commandments. If we love the Lord Jesus and keep his commandments, no animal will be able to do us any harm." The monk departed greatly edified.