On 17 October 1521, Pope Leo X declared King Henry VIII the Fidei Defensor or Defender of the Faith. This title was given to honor Henry for his book Defense of the Seven Sacraments which attacked the theology of Martin Luther and was dedicated to Leo. This title was added to the full royal title of Henry as “Henry the Eighth, by the Grace of God, King of England and France, Defender of the Faith and Lord of Ireland”.
After Henry VIII broke with the Catholic Church, Pope Paul III excommunicated Henry and rescinded the grant of the title “Defender of the Faith” in 1538 but the English Parliament declared that the title remained valid.
Henry’s book was very popular and went through twenty editions in the sixteenth century.