John Wycliffe (; also spelled Wyclif, Wickliffe, and other variants; c. 1328 – 31 December 1384) was an English scholastic philosopher, theologian, biblical translator, reformer, Catholic priest, and a seminary professor at the University of Oxford. He became an influential dissident within the Catholic priesthood during the 14th century and is considered an important predecessor to Protestantism. Wycliffe questioned the privileged status of the clergy, who had bolstered their powerful role in England, and the luxury and pomp of local parishes and their ceremonies.

Wycliffe advocated translation of the Bible into the common vernacular. According to tradition, Wycliffe is said to have completed a translation direct from the Vulgate into Middle English – a version now known as Wycliffe's Bible. While it is probable that he personally translated the Gospels of Matthew, Mark, Luke, and John, it is possible he translated the entire New Testament. At any rate, it is assumed that his associates translated the Old Testament. Wycliffe's Bible appears to have been completed prior to 1384 with additional updated versions being done by Wycliffe's assistant John Purvey, and others, in 1388 and 1395. More recently, historians of the Wycliffite movement have suggested that Wycliffe had at most, a minor role in the actual translations.

Wycliffe's later followers, derogatorily called Lollards by their orthodox contemporaries in the 15th and 16th centuries, adopted many of the beliefs attributed to Wycliffe such as theological virtues, predestination, iconoclasm, and the notion of caesaropapism, while questioning the veneration of saints, the sacraments, requiem masses, transubstantiation, monasticism, and the legitimacy of the Papacy. Like the Waldensians, Hussites and Friends of God, the Lollard movement in some ways anticipated the Protestant Reformation. Wycliffe was accordingly characterised as the "evening star" of scholasticism and as the morning star or stella matutina of the English Reformation, an epithet first accorded to the theologian by the 16th century historian and controversialist John Bale in his Illustrium maioris britanniae scriptorum (Wesel, 1548).

Wycliffe's writings in Latin greatly influenced the philosophy and teaching of the Czech reformer Jan Hus (c. 1369–1415), whose execution in 1415 sparked a revolt and led to the Hussite Wars of 1419–1434.