Martin Luther (1483-1546), German theologian and reformer, was an important figure in the initial development of Protestantism. After entering the Catholic priesthood in 1507, Luther pursued theological studies at the University of Wittenberg, where he later became a professor. He also served as a preacher at a parish church and as a district vicar of the Augustinian order.
Luther came to reject the customs of the established church and instead ascribed moral authority solely to the scriptures, avowing "justification by faith alone." He strongly objected to the church’s sale of indulgences as a means of repentance, a practice associated with corruption, and voiced this challenge in the Ninety-Five Theses, which he posted on the door of the Wittenberg castle church on October 31, 1517.