In the late 1130s, Arnold of Brescia, an Italian canon regular became one of the first theologians to attempt to reform the Roman Catholic Church. After his death, his teachings on apostolic poverty gained currency among Arnoldists, and later more widely among Waldensians and the Spiritual Franciscans, though no written word of his has survived the official condemnation. In the early 1170s, Peter Waldo founded the Waldensians. He advocated an interpretation of the Gospel that led to conflicts with the Roman Catholic Church. By 1215, the Waldensians were declared heretical and subject to persecution. Despite that, the movement continues to exist to this day in Italy, as a part of the wider Reformed tradition.

Who was one of the first to try to reform the Catholic Church?