FLACIUS, MATTHIAS (1520–1575), known as Matthias Flacius Illyricus, was an Italo-Croatian scholar and polemicist; a creative, fiery theological leader of the late Lutheran Reformation. Born in Albona, Istria, Flacius was trained in the humanist schools of Venice under the influence of his uncle, the Franciscan provincial Baldo Luperino, who was sympathetic to Lutheranism. Flacius studied at Tübingen before moving to Wittenberg, where Luther's intervention in a personal religious crisis confirmed Flacius as his passionately committed disciple. The defeat of Lutheran princes in the Smalcald War ended Flacius's career as a Hebrew instructor at Wittenberg and propelled him into the leadership of the Gnesio-Lutheran party, formed by Luther's more radical disciples in opposition to the imposition of the Augsburg Interim (1548) and the compromise settlement worked out by other Lutheran leaders, the Leipzig Interim (1548). Flacius's historical and liturgical research, as well as his biblical, lay-oriented argumentation, led him...