Thomas Cranmer (2 July 1489 21 March 1556) was a leader of the English Reformation and Archbishop of Canterbury during the reigns of Henry VIII, Edward VI and, for a short time, Mary I. He helped build the case for the annulment of Henry's marriage to Catherine of Aragon, which was one of the causes of the separation of the English Church from union with the Holy See. Along with Thomas Cromwell, he supported the principle of royal supremacy, in which the king was considered sovereign over the Church within his realm.

During Cranmer's tenure as Archbishop of Canterbury, he was responsible for establishing the first doctrinal and liturgical structures of the reformed Church of England. Under Henry's rule, Cranmer did not make many radical changes in the Church, due to power struggles between religious conservatives and reformers. He published the first officially authorised vernacular service, the Exhortation and Litany.

When Edward came to the throne, Cranmer was able to promote major reforms. He wrote and compiled the first two editions of the Book of Common Prayer, a complete liturgy for the English Church. With the assistance of several Continental reformers to whom he gave refuge, he changed doctrine or discipline in areas such as the Eucharist, clerical celibacy, the role of images in places of worship, and the veneration of saints. Cranmer promulgated the new doctrines through the Prayer Book, the Homilies and other publications.

After the accession of the Catholic Mary I, Cranmer was put on trial for treason and heresy. Imprisoned for over two years and under pressure from Church authorities, he made several recantations and apparently reconciled himself with the Catholic Church. While this would have normally absolved him, Mary wanted him executed, and, on the day of his execution, he withdrew his recantations, to die a heretic to Catholics and a martyr for the principles of the English Reformation. Cranmer's death was immortalised in Foxe's Book of Martyrs and his legacy lives on within the Church of England through the Book of Common Prayer and the Thirty-Nine Articles, an Anglican statement of faith derived from his work.

The archbishop of Canterbury is the senior bishop and principal leader of the Church of England, the symbolic head of the worldwide Anglican Communion and the diocesan bishop of the Diocese of Canterbury. The current archbishop is Justin Welby, who was enthroned at Canterbury Cathedral on 21 March 2013. Welby is the 105th in a line which goes back more than 1400 years to Augustine of Canterbury, the "Apostle to the English", sent from Rome in the year 597. Welby succeeded Rowan Williams.From the time of Augustine until the 16th century, the archbishops of Canterbury were in full communion with the See of Rome and usually received the pallium from the pope. During the English Reformation, the Church of England broke away from the authority of the pope. Thomas Cranmer became the first holder of the office following the English Reformation in 1533, while Reginald Pole was the last Roman Catholic in the position, serving from 1556 to 1558 during the Counter-Reformation. In the Middle Ages there was considerable variation in the methods of nomination of the archbishop of Canterbury and other bishops. At various times the choice was made by the monks of the Cathedral Priory (before the Dissolution of the Monasteries under Henry VIII), the pope, or the king of England. Since the English Reformation, the Church of England has been more explicitly a state church and the choice is legally that of the Crown; today it is made by the reigning monarch on the advice of the prime minister, who in turn receives a shortlist of two names from an ad hoc committee called the Crown Nominations Commission.