Proto-Protestantism, also called pre-Protestantism or pre-Reformation movements, refers to individuals and movements that propagated ideas similar to Protestantism before 1517, which historians usually regard as the starting year for the Reformation era. Major representatives of proto-Protestantism include Peter Waldo (c. 1140 – c. 1205), John Wycliffe (1320s–1384), Jan Hus (c. 1369 – 1415) and the movements they started.
The Waldensians had adopted ideas that in the late 1130s, Arnold of Brescia, an Italian canon regular, had developed in a first attempt to reform the Roman Catholic Church. His teachings on apostolic poverty gained currency among Arnoldists. By 1215, the Waldensians were declared heretical and subject to persecution.
Beginning in the first decade of the 15th century, Jan Hus, a Czech Catholic priest and professor who was influenced by John Wycliffe's writings, founded the Hussite movement. He was burned at the stake as a heretic in 1415. After his execution, a revolt erupted. Hussites defeated five continuous crusades proclaimed against them by the Pope.
Later on, theological disputes caused a split within the Hussite movement. Utraquists maintained that both the bread and the wine should be administered to the people during the Eucharist. Another major faction were the Taborites, who opposed the Utraquists in the Battle of Lipany during the Hussite Wars. There were two separate parties among the Hussites: moderate and radical movements. Other smaller regional Hussite branches in Bohemia included Adamites, Orebites, Orphans and Praguers.
Less influential early reformers
Throughout the Middle Ages, there were many Christian sects, cults and movements whose teachings foreshadowed later Protestant movements. Some of the main groups were:
Tondrakians – an Armenian group (9th to 11th centuries) who advocated the abolition of the Church along with all its traditional rites.
Bogomils – a group arising in the 10th century in Bulgaria,Macedonia and the Balkans who sought a return to the spirituality of the early Christians and opposed established forms of government and church. The Bogomils were heavily dualist, and bore similarities to ancient Gnosticism.
Cathars, or Albigensians — self-identified as Good Christians, the Cathars were a 12th-14th century sect influenced by the teachings of the Bogomils and Paulicians. Aside from their Gnostic influences, they rejected the spiritual authority of the priesthood and the efficacy of the sacraments. Catharism was heavily suppressed following the Albigensian Crusade, during which the majority of Cathars were killed.
Apostolic Brethren (later known as Dulcinians) – a 13th- to 14th-century sect from northern Italy founded by Gerard Segarelli and continued by Fra Dolcino of Novara. The Apostolic Brethren rejected the worldliness of the church and sought a life of perfect sanctity, in complete poverty, with no fixed domicile, no care for the morrow, and no vows.
Fraticelli, or Spiritual Franciscans — An extreme group of Franciscans, active from the 13th to 15th centuries. The Fraticelli held that the Catholic hierarchy had become corrupt and illicit by way of its wealth and worldliness, and that everyone who was a part of it was damned.
Barnett, S. J. (1999). "Where Was Your Church before Luther? Claims for the Antiquity of Protestantism Examined". Church History. Cambridge University Press. 68 (1): 14–41. doi:10.2307/3170108. ISSN0009-6407. JSTOR3170108.
Stephen D. Bows: Reform before the Reformation : Vincenzo Querini and the religious Renaissance in Italy, Leiden [et al.], 2002.
Walter Rügert: John Wyclif, Jan Hus, Martin Luther: Wegbereiter der Reformation Konstanz, 2017.