Ronald Knox died on August 24, 1957. He was an Anglo-Catholic who converted to Catholicism (it was a serious enough matter that he had to quit his job and his father disinherited him) and began writing detective fiction. He was one of the founding members of the Detection Club, along with Agatha Christie, Dorothy Sayers, Baroness Emma Orczy, and G. K. Chesterton, among others. This club was the core of the Golden Age of Detective Fiction, and its code of authorial ethics was written up by Knox as a Decalogue:
1. The criminal must be mentioned in the early part of the story, but must not be anyone whose thoughts the reader has been allowed to know.
2. All supernatural or preternatural agencies are ruled out as a matter of course.
3. Not more than one secret room or passage is allowable.
4. No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.
5. No Chinaman must figure in the story.
6. No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.
7. The detective himself must not commit the crime.
8. The detective is bound to declare any clues which he may discover.
9. The "sidekick" of the detective, the Watson, must not conceal from the reader any thoughts which pass through his mind: his intelligence must be slightly, but very slightly, below that of the average reader.
10. Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.
Members of the club generally adhered to the rules of the game, although some (like Chesterton) liked to experiment in how to bend or break them. The reason for the rules was that members of the Detection Club saw themselves as participants in a great game, and the game was one whose primary point (as Knox pointed out) was to lay out and unravel a mystery; to be a proper mystery, elements have to be added clearly and early that are suitable for arousing curiosity, and the mystery actually has to be unraveled. In "Studies in the Literature of Sherlock Holmes," Knox was also the inventor of the Great Game, in which one takes the Sherlock Holmes stories and treats them as historical documents.
In addition to detective fiction, Knox translated the Vulgate, the Imitation of Christ, and Therese de Lisieux's Autobiography of a Soul; he also wrote a number of excellent works of Catholic apologetics. Knox's approach is very similar to Chesterton's, although more measured; Knox became Catholic because of things Chesterton had written while still Anglican, and Knox's Catholic writings influenced Chesterton when Chesterton became Catholic. Knox delivered the homily at Chesterton's funeral.
He died of cancer. Evelyn Waugh was his literary executor and first biographer.
You can get something of what Knox was like by saying that he was something like each of his three brothers. Dilwyn Knox was a classics scholar who was one of Britain's foremost cryptanalysts; Edmund Knox was a satirist who was editor of Punch; and Wilfred Knox was a New Testament scholar and (Anglican) monk.
Some Knox works online:
The Belief of Catholics
"Reunion All Round" from Essays in Satire
"Studies in the Literature of Sherlock Holmes" from Essays in Satire