 Henry's son and successor, Duke Maurice, was one of the most controversial figures of the Reformation period.Although a zealous Protestant, ambition and desire to increase his wealth led him to join the Emperor against the Schmalkaldic League, established by his "Ernestine" cousin, John Frederick.After the outbreak of the Schmalkaldic War Elector John Frederick was placed under an Imperial ban and was finally defeated and captured by Emperor Charles V at the Battle of Mühlberg on 24 April 1547.