Fidei Defensor is one of the Monarch's titles that go back to Henry V111.
In the early part of his reign 'ole 'enry was an energetic young man and a good (politically) Christian who was highly regarded by the Church of Rome. The Pope awarded him the title of 'Defender of the Faith'.
He had dreadful disagreements with the Church of Rome later on, when he wanted a divorce from his first wife Catherine of Aragon, who was a good Spanish Lady who was also highly regarded by the Church of Rome.
The Church of Rome vehemently disagreed with what 'ole 'enry wanted, and refused to annul the marriage. 'Ole 'enry then divorced the English branch of the Church from the Church of Rome, and set up the Church of England as a state Church, so the Pope's rulings no longer applied to him. The State church was known as an established church, that is, one sponsored by the State.
He went ahead with the divorce, and married Anne Boleyn, who became the mother of Edward V1. She later had her head chopped off. 'Ole 'enry went on to have six wives, and some of them also met a sticky end. In his later years, he was really a selfish and cruel tyrant. He possibly suffered from syphilis later in life.
He was known as 'Old Copper Nose' for his seriously debased silver coinage, because on his facing portrait, the tip of his nose wore through, revealing the copper rich alloy underneath.
Interestingly, the title 'Defender of the Faith' was an
inherited one and has been carried on by all monarchs to this present day. Hence 'Fidei Defensor' - or F.D.
And now for the word of the week:
Antidisestablishmentarianism: The political movement to resist the Church from not being an established Church.