Matthias Flacius (originally Vlacich), Matthias, sur-named Illyricus, a German Protestant theologian, born at Albona, Istria, about 1520, died in Frankfort in 1575. He was induced to abandon his original intention of entering a convent, and to visit the German universities. At Wittenberg he heard Luther and Melanchthon, adopted their opinions, and was appointed professor of Hebrew. After the death of Luther he resisted the formulary known as the Interim, opposed the conciliatory measures of Melanchthon, and established himself at Magdeburg at the head of a party of rigid Lutherans. In 1558 he was appointed professor of theology in the newly founded university of Jena, and engaged in a violent dispute with Strigel concerning hereditary sin and the synergetic power of the human will, which resulted in his being deposed. He retired to Ratisbon, and afterward preached in several German cities. He was one of the most prominent of the reformers, and besides producing numerous polemical writings, distinguished for their severity, was the originator and one of the principal authors of the famous " Centuries of Magdeburg."