John Chrysostom (so called from chrysostomos, "golden-mouthed", because of his eloquence), was a Doctor and Patriarch of the Catholic Church. He was born at Antioch around 347 CE and died at Commana in Pontus in 407 CE. In 398 CE he was ordained Bishop of Constantinople.
Chrysostom's connection to the bestiary is the mistaken identity of him as the author of the Physiologus, an honor he shared with other eastern ecclesiastics of his time. He in fact had nothing to do with that text. The work attributed to him was commonly known as the Dicta Chrysostomi (the sayings of Chrysostom); the text usually begins "Incipiunt dicta Johannis Crisostomi de naturis bestiarium". It is thought that the Dicta Chrysostomi text actually originated in France around 1000 CE. It is similar to the "B" version of the Physiologus, but divides its chapters (usually 27) into those on beasts and those on birds. Gervaise, in his French rhymed bestiary of the thirteenth century, credits Chrysostom as the author of the text that he translated. Chrysostom is also ascribed authorship in two copies of the Bestiaire of Pierre de Beauvais.