"AZATHOTH—hideous name" reads a note HP Lovecraft is popularly supposed to have scribbled to himself in around 1919. It is thought that the moniker is at least partially inspired by Azazel- a term used in Christianity, Judaism & Islam to denote a demon or fallen angel, & can also be translated as scapegoat. As in Leviticus:
"Aaron shall offer the bull as a sin offering for himself and shall make atonement for himself and for his house.Then he shall take the two goats and set them before the Lord at the entrance of the tent of meeting. And Aaron shall cast lots over the two goats, one lot for the Lord and the other lot for Azazel. And Aaron shall present the goat on which the lot fell for the Lord and use it as a sin offering, but the goat on which the lot fell for Azazel shall be presented alive before the Lord to make atonement over it, that it may be sent away into the wilderness to Azazel."The theological aspect seems to have stuck with Lovecraft, as later in 1919 he had his first idea for a story to feature his creation.
"A terrible pilgrimage to seek the nighted throne of the far daemon-sultan Azathoth."Of course the Doctor has previous experience when it comes to Daemons!
The first Lovecraftian work to mention the 'daemon-sultan' was The Dream-Quest Of Unknown Kadath.
"Outside the ordered universe is that amorphous blight of nethermost confusion which blasphemes and bubbles at the center of all infinity—the boundless daemon sultan Azathoth, whose name no lips dare speak aloud, and who gnaws hungrily in inconceivable, unlighted chambers beyond time and space amidst the muffled, maddening beating of vile drums and the thin monotonous whine of accursed flutes."Time, space & ''accursed flutes''? It's not recorded if the Second Doctor was present, but if so the Third Doctor might agree with the Old One's assessment of his previous self's playing.
Possibly not entirely coincidentally Jo Grant also dubbed the beloved recorder a flute........but by the time of All-Consuming Fire, the Doctor has forgotten all about the handy musical accompaniment to his thinking as he's in his Seventh incarnation.
In the midst of returning a few books overdue from way back in his First body to the Library of St John The Beheaded, the Doctor is called upon to investigate a spate of thefts including that of the Necronomicon itself!
And whoever the thief may be is seeking to summon Azathoth, who waits to cross over to Earth from his prison on Ry'leh, a planet named after the watery domain of Cthulhu himself! It's established that the Silurians worshiped him as a god during their time walking the Earth.
The Doctor is also kind enough to confirm that those Old Ones we've already looked at are well within their rights to be included in the pantheon. Lovecraft again refers to the one true ' original' Old One besides Cthulhu in The Whisperer In Darkness, The Dreams In The Witch-House & The Haunter Of The Dark.
It would be churlish not to mention the men assisting the Doctor & Ace- no less than Sherlock Holmes & Doctor Watson! Lets have a look at a summary from www.schoolandholmes.com:
"Holmes and Watson are returning from a visit to Vienna aboard the Orient Express. The train is stopped and they are taken aboard another, where they are commissioned by the Pope to locate books missing from the Library of St. John the Beheaded. In London, they visit the Library, where Watson sees a hooded figure disappearing through a door which Holmes later finds to be locked. Returning to Baker Street, they find the Doctor waiting for them and reluctantly agree to work together. Watson and the Doctor visit Kate Prendersly, a patron of the library, who tells them of a time she saw a man eating books. Before she can go on, her body bursts into flames.It seems there's a grain of truth to the idea of the Library, too. The Catholic Church did indeed formerly have a list of prohibited tomes, the Index Librorum Prohibitorum or ' List Of Prohibited Books' as sworn in by Pope Paul IV in 1559! Amazingly it was in force until 1966 when another Pope Paul, the VI, formally abolished it.
Meanwhile, Holmes visits Hackney Marshes, where the library guards are being punished, and witnesses a dogfight between three dogs and the Giant Rat of Sumatra, a strange three-legged creature. Later, in a meeting with Mycroft, Watson meets Holmes older brother, Sherringford, who reveals that it is the diaries of their father, Siger Holmes, that have been stolen, containing information about a means of passing from this world into others.
Holmes, Watson and the Doctor set sail aboard the S.S. Matilda Briggs for India, the site of Siger's experiences, where they meet up with Bernice. The Doctor is carried off by a Rakshassa, and Holmes, Watson and Bernice travel on in pursuit of Baron Maupertuis to Jabhalabad, where they stay with Colonel Warburton.
On a visit to the Nizam's Palace, where they meet Lord John Roxton and a missionary named O'Connor, they are taken prisoner by Maupertuis, and led to a cave temple, where, as the portal opens up to the planet Ry'leh, they are attacked by Rakshassi, and O'Connor's true identity is revealed, Maupertuis and his men escape through the portal and it closes behind them. Eventually, Holmes and his companions manage to reopen the portal and pass through to the planet Ry'leh, where they must confront Azathoth, and learn the truth about his human assistants."
But if you're interested in prohibited reading then take a look at the 1948 version/list here!