Leontius of Byzantium (Greek: Λεόντιος, 485–543) was a Byzantine Christian monk and the author of an influential series of theological writings on sixth-century Christological controversies.
The first scholar to identify and challenge the ambiguity of the writings that come down to us under the name of "Leontius" was Friedrich Loofs in 1887, arguing for a single author of the corpus leontianum.
[1]: 7 Brian Daley, however, considers this association very tenuous, both for historical reasons and because the text of the corpus leontianum does not seem to contain Origenist views.
[1]: 6 From the introduction of his third treatise Against the Nestorians we learn that as a young man, he was a member of the circle of Diodorus of Tarsus and Theodore of Mopsuestia.
[1]: 5 According to Carlo Dell'Osso, the first scholar to translate his writings into a modern language,[1] his theology is dominated by the theme of diphysitism (a reaction to the heretical doctrine of monophysitism), which is an affirmation of the permanence and distinction of the two natures of Christ — divine and human — after the Incarnation, a condition which Leontius identified as hypostatic union.