John Italus or Italos (Greek: Ἰωάννης ὁ Ἰταλός, Iōannēs o Italós; Latin: Johannes Italus) was a NeoplatonicByzantine philosopher of the eleventh century. He was Calabrian in origin, his father being a soldier. He came to Constantinople, where he became a student of Michael Psellus in classical Greek philosophy. He succeeded Psellus in his position as head of the philosophical school. Subsequently, he came into conflict with Diogenes, and he was condemned in 1082 by Patriarch Cosmas I of Constantinople for heresy.
John Italus was born in Italy from where he derived his name. He was the son of an Italian, who was engaged as an auxiliary in an attempt by the Sicilians to withdraw from their subjection to the Byzantine emperor, and took with him his son, then a child, who thus spent his early years, not in the schools, but the camp. When the Byzantine commander, George Maniaces, revolted against Constantine X Doukas in 1042, the father of Italus fled back to Italy with his son, who after a time found his way to Constantinople. He had already made some attainments, especially in logic. At Constantinople he pursued his studies under several teachers, and last under Michael Psellus; with whom, however, he soon quarrelled, not being able, according to Anna Comnena, to enter into the subtleties of his philosophy, and being remarkable for his arrogance and disputatious temper. He is described as having a commanding figure, being moderately tall and broad-chested, with a large head, a prominent forehead, an open nostril, and well-knit limbs.