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.