John Knox (c. 1514 – 24 November 1572) was a Scottish minister, Reformed theologian, and writer who was a leader of the country's Reformation. He was the founder of the Church of Scotland.

Born in Giffordgate, a street in Haddington, East Lothian, Knox is believed to have been educated at the University of St Andrews and worked as a notary-priest. Influenced by early church reformers such as George Wishart, he joined the movement to reform the Scottish Church. He was caught up in the ecclesiastical and political events that involved the murder of Cardinal David Beaton in 1546 and the intervention of the regent Mary of Guise. He was taken prisoner by French forces the following year and exiled to England on his release in 1549.

While in exile, Knox was licensed to work in the Church of England, where he rose in the ranks to serve King Edward VI of England as a royal chaplain. He exerted a reforming influence on the text of the Book of Common Prayer. In England, he met and married his first wife, Margery Bowes. When Queen Mary I ascended the throne of England and re-established Catholicism, Knox was forced to resign his position and leave the country. Knox moved to Geneva and then to Frankfurt. In Geneva, he met John Calvin, from whom he gained experience and knowledge of Reformed theology and presbyterian polity. He created a new order of service, The Forme of Prayers, which was eventually adopted by the Reformed Church in Scotland and came to be known as the Book of Common Order. It was the first book printed in any Gaelic language. Knox left Geneva to head the English refugee church in Frankfurt but he was forced to leave over differences concerning the liturgy, thus ending his association with the Church of England.

On his return to Scotland, Knox led the Protestant Reformation in Scotland, in partnership with the Scottish Protestant nobility. The movement may be seen as a revolution since it led to the ousting of Mary of Guise, who governed the country in the name of her young daughter Mary, Queen of Scots. Knox helped write the new confession of faith and the ecclesiastical order for the newly created Reformed Church, the Kirk. He wrote his five-volume The History of the Reformation in Scotland between 1559 and 1566. He continued to serve as the religious leader of the Protestants throughout Mary's reign. In several interviews with the Queen, Knox admonished her for supporting Catholic practices. After she was imprisoned for her alleged role in the murder of her husband Lord Darnley, and King James VI was enthroned in her stead, Knox openly called for her execution. He continued to preach until his final days.

John Knox was born sometime between 1505 and 1515 in or near Haddington, the county town of East Lothian. His father, William Knox, was a merchant. All that is known of his mother is that her maiden name was Sinclair and that she died when John Knox was a child. Their eldest son, William, carried on his father's business, which helped in Knox's international communications.

Knox was probably educated at the grammar school in Haddington. At this time, the priesthood was the only path for those whose inclinations were academic rather than mercantile or agricultural. He proceeded to further studies at the University of St Andrews or possibly at the University of Glasgow. He studied under John Major, one of the greatest scholars of the time. Knox was ordained a Catholic priest in Edinburgh on Easter Eve of 1536 by William Chisholm, Bishop of Dunblane.

Knox first appears in public records as a priest and a notary in 1540. He was still serving in these capacities as late as 1543 when he described himself as a "minister of the sacred altar in the diocese of St Andrews, notary by apostolic authority" in a notarial deed dated 27 March. Rather than taking up duties as a parish priest, Knox became tutor to two sons of Hugh Douglas of Longniddry. He also taught the son of John Cockburn of Ormiston. Both of these lairds had embraced the new religious ideas of the Reformation.

Knox did not record when or how he was converted to the Protestant faith, but perhaps the key formative influences on Knox were Patrick Hamilton and George Wishart. Wishart was a reformer who had fled Scotland in 1538 to escape punishment for heresy. He first moved to England, where in Bristol he preached against the veneration of the Virgin Mary. He was forced to make a public recantation and was burned in effigy at the Church of St Nicholas as a sign of his abjuration. He then took refuge in Germany and Switzerland. While on the Continent, he translated the First Helvetic Confession into English. He returned to Scotland in 1544, but the timing of his return was unfortunate. In December 1543, James Hamilton, Duke of Châtellerault, the appointed regent for the infant Mary, Queen of Scots, had decided with the Queen Mother, Mary of Guise, and Cardinal David Beaton to persecute the Protestant sect that had taken root in Scotland. Wishart travelled throughout Scotland preaching in favour of the Reformation, and when he arrived in East Lothian, Knox became one of his closest associates. Knox acted as his bodyguard, bearing a two-handed sword in order to defend him. In December 1545, Wishart was seized on Beaton's orders by the Earl of Bothwell and taken to the Castle of St Andrews. Knox was present on the night of Wishart's arrest and was prepared to follow him into captivity, but Wishart persuaded him against this course saying, "Nay, return to your bairns [children] and God bless you. One is sufficient for a sacrifice." Wishart was subsequently prosecuted by Beaton's Public Accuser of Heretics, Archdeacon John Lauder. On 1 March 1546, he was burnt at the stake in the presence of Beaton.