Syagrios was a thug working for Thanasioi rebel leader Livanios. Along with Livanios' daughter, Olyvria, he abducted Phostis, the son of Videssian ruler Krispos. He served as Phostis' guard; he was skeptical of Phostis' flirting with the Thanasioi heresy until the young man seemingly charged an Imperial cavalry unit and was wounded, after which Syagrios was convinced. Olyvria escaped with Phostis from Syagrios' clutches, which enraged the thug, who tried to murder the pair in their tent after they were married. He was quickly dispatched by a Halogai imperial guardsman.