John Wycliffe (/ˈwɪklɪf/; also spelled Wyclif, Wickliffe, Wicklyf etc.; c. 1328 – 31 December 1384) was an English scholastic philosopher, Christian reformer, Catholic priest, and a theology professor at the University of Oxford. Wycliffe is traditionally believed to have advocated for or made a vernacular translation of the Vulgate Bible into Middle English, though more recent scholarship has minimised the extent of his advocacy or involvement for lack of direct contemporary evidence.

He became an influential dissident within the Catholic priesthood during the 14th century and his ideas are often considered an important predecessor to Protestantism. His political-theological theory of dominion meant that the church was not allowed to own property or have ecclesiastic courts, and men in mortal sin were not entitled to exercise authority in the church or state, nor to own property. Wycliffe insisted on the radical poverty of all clergy.

Wycliffe has been characterised as the "evening star" of scholasticism and as the "morning star" or stella matutina of the English Reformation.

Certain of Wycliffe's later followers, derogatorily called Lollards by their orthodox contemporaries in the 15th and 16th centuries, adopted a number of the beliefs attributed to Wycliffe such as theological virtues, predestination, iconoclasm, and the notion of caesaropapism, with some questioning the veneration of saints, the sacraments, requiem masses, transubstantiation, monasticism, and the legitimacy or role of the Papacy. Wycliffe's writings in Latin greatly influenced the philosophy and teaching of the Czech reformer Jan Hus (c. 1369–1415).

Wycliffe was born in the village of Hipswell, near Richmond in the North Riding of Yorkshire, England, although there is some dispute about the date. He has conventionally been given a birth date of 1324^{[citation needed]} but Hudson and Kenny state only records "suggest he was born in the mid-1320s" and Conti states that he was born "after 1331".

Wycliffe received his early education close to his home. It is unknown when he first came to Oxford, with which he was so closely connected until the end of his life, but he is known to have been at Oxford around 1345. Thomas Bradwardine was the Archbishop of Canterbury and his book On the Cause of God Against the Pelagians, a bold recovery of the Pauline–Augustinian doctrine of grace, greatly shaped young Wycliffe's views, as did the Black Death, which reached England in the summer of 1348. From his frequent references to it in later life it appears to have made a deep and abiding impression upon him. According to Robert Vaughn, the effect was to give Wycliffe "very gloomy views in regard to the condition and prospects of the human race". In September 1351, Wycliffe became a priest. Wycliffe would have been at Oxford during the St Scholastica Day riot, in which sixty-three students and a number of townspeople were killed.

In 1356, Wycliffe completed his bachelor of arts degree at Merton College as a junior fellow. That same year he produced a small treatise, The Last Age of the Church. In the light of the virulence of the plague, which had subsided seven years previously, Wycliffe's studies led him to the opinion that the close of the 14th century would mark the end of the world. While other writers viewed the plague as God's judgement on sinful people, Wycliffe saw it as an indictment of an unworthy clergy. The mortality rate among the clergy had been particularly high and those who replaced them were, in his opinion, uneducated or generally disreputable.

In 1361, he was Master of Balliol College in Oxford. That year he was presented by the college to the parish of Fillingham in Lincolnshire, which he visited rarely during long vacations from Oxford. For this he had to give up the headship of Balliol College, though he could continue to live at Oxford. He is said to have had rooms in the buildings of The Queen's College. In 1362, he was granted a prebend at Aust in Westbury-on-Trym, which he held in addition to the post at Fillingham.