John Fisher (1469–1535) served as Bishop of Rochester from 1505 until his removal from office by Henry VIII and execution in 1535. Fisher initially enjoyed a close relationship with the court, and may have advised the king in writing the Assertio septem sacramentorum against Martin Luther (see RCIN 1006836).

However, when Henry began to seek a divorce from his wife Catherine of Aragon, Fisher gave the queen his full support. De causa matrimonii serenissimi Angliae Regis is one of Fisher’s eight written defences of the marriage—the only one to be published, from a manuscript smuggled out of England. The treatise refutes Henry’s declaration that his marriage to Catherine was illegal due to her previous marriage to his elder brother, Arthur, Prince of Wales.

In April 1534, Fisher refused the oath to the king and was imprisoned in the Tower of London. In May 1535, he was created a Cardinal by Pope Paul III and was beheaded the following month. Fisher’s execution made him a martyr in the eyes of many Roman Catholics, who saw parallels with his death and that of his namesake, St John the Baptist. He was canonised, along with Sir Thomas More, by Pope Pius XI in 1935.