Sebastian Franck was a 16th-century German freethinker, humanist, and radical reformer.

The Radical Reformation represented a response to perceived corruption both in the Catholic Church and in the expanding Magisterial Protestant movement led by Martin Luther and many others. Beginning in Germany and Switzerland in the 16th century, the Radical Reformation gave birth to many radical Protestant groups throughout Europe. The term covers Radical Reformers like Thomas Müntzer and Andreas Karlstadt, the Zwickau prophets, and Anabaptist groups like the Hutterites and the Mennonites.