Flacius or Vlacich, Matthias, surnamed Illyricus, a German theologian, born at Albona, in Illyria; was the pupil of Luther and Melanchthon; became professor of the Old Testament Scriptures at Wittenberg, but four years later lost his position on account of certain attacks he made on Melanchthon; subsequently he was elected professor at Jena, but was again deposed for heterodox notions on original sin; died in poverty; was author of an ecclesiastical history and other works (1520-1575).