Sherringford Holmes

Sherringford Holmes was the eldest brother of Sherlock Holmes and Mycroft Holmes, and held by them to possess an even greater intellect than either. Late in his life, he entered the service of an entity claiming to be the Great Old One Azathoth and attempted to help her invade the Earth, crossing paths with the Seventh Doctor, Bernice Summerfield and Ace in the process.

Physical appearance
In his natural form, Sherringford Holmes bore a strong resemblance to his brother Sherlock, possessing the same aquiline face and demeanour, but his eyes were mild and brown like Mycroft's. His hair was grey and close-cropped, and he was taller and thinner than either of his brothers.

As a follower of Azathoth, Sherringford was also branded with the Mark of Azathoth, which incited him to be transubstantiated into a rakshassa. To facilitate his dealings with humans leading up to the completion of his plans, he held back most of the transformation, though he could not stop his hands becoming clawed, reddish and vein-riddled, forcing him to wear white gloves at all times.

He eventually completed the transformation once he knew the cat to be out of the bag as far as Sherlock and the Doctor were concerned, becoming a large and indistinct-looking rakshassa, though he kept on his tattered, white ceremonial robes, unlike most rakshassi, who went unclothed. (PROSE: All-Consuming Fire)

Early life
The son of Siger Holmes, Sherringford Holmes was thirteen years older than Mycroft, and around twenty years older than Sherlock; he would retain a habit of referring to both as "my dear boy" well into the three siblings' adulthood. Sherringford knew Sherlock to have been "an impetuous youth" and Mycroft "always well-fed", characteristics which it amused Sherringofrd to note their adult selves still displayed. (PROSE: All-Consuming Fire)

Adulthood
Sherringford chose to spend his days in the North Riding of Yorkshire, in the Holmes family's old farmstead, carrying on the family tradition as a squire while his brothers "preferred the attractions of London". He employed his extraordinary intellect for nothing more than crop rotation and sheep breeding. He additionally made a hobby of researching the history of the Holmes family, and had "some success" tracing it back to Norman roots, also confirming the old family legend that a distant relative of the family married the Commander in Chief of the Naval Forces of His Holiness the Pope during the last century. He wrote regularly to Sherlock, who only intermittently read these letters. (PROSE: All-Consuming Fire)

The herald of Azathoth
In the diaries of his father Siger Holmes, which he was allowed to consult by Mycroft Holmes even though they were kept in the Vatican's secure Library of St John the Beheaded, Sherringford Holmes discovered the religion of the Great Old One Azathoth. Entering the service of the supposed Azathoth imprisoned on the planet Ry'leh, he converted fully to her religion, believing her to have been the creator of the universe and other such tenets of Azathoth's faith in which the Doctor put little stock.

As a follower of Azathoth, he was branded with the Mark of Azathoth, beginning to mutate into a rakshassa. However, he held off his transubstantiation (despite his growing distaste for his lowly, "debased" human form) until it was no longer necessary for him to be able to pass for an ordinary human.

In the guise of a mysterious hooded figure, Sherringford contacted the wealthy Baron Maupertuis, entrusting him with the secret of the chant which would open up a gateway to Ry'leh, but claiming that his purpose was to have humanity conquer Ry'leh in the name of the British Empire. In truth, the army of low-lifes whom Maupertuis brought to Ry'leh was intended to distract the Shlangii garrisons placed on Ry'leh as guards while Sherringford and the other rakshassi spirited Azathoth off to Earth unnoticed.

Learning that his brother had been hired by the Pope to investigate the theft of the occult books from the Library of St John the Beheaded by Maupertuis, Sherringford had an interview with Sherlock and Mycroft, during which he also encountered John Watson for the first time; Sherlock had never told Watson of Sherringford's existence until that point. Sherringford introduced them to one of the Shlangii loyal to Azathoth, K'tcar'ch, whom he had claim his species was native to Ry'leh and a race of peaceful philosophers threatened by Maupertuis's imperalist delusions of grandeur and warlike designs.

However, he revealed himself to Sherlock and Watson (now joined by the Seventh Doctor, Bernice Summerfield and Ace) once the investigators reached Azatoth's sanctum on Ry'leh, and, finally letting go of his human form, was present as a rakshassa when the Doctor confronted Azathoth, still acting as her second-in-command. To the Doctor's claim that this Azathoth was not the real Azathoth but an impostor of far lesser power, Sherringford angrily answered that he was simply clutching at straws of explanation.

The Doctor and Ace then interfered with the dimension-ripping chant, causing Azathoth and the rakshassi to not be transported in India as they had intended, but rather in San Francisco on the day and place of the great earthquake. Sherringford realised that something had gone wrong but dared not disappoint his god, and so led the rakshassa charge forward anyway. Standing in the Palace Hotel's lobby where they had all materialised, Sherringford began to intone "My brothers…" before a large gout of flame blew in from the kitchen as the Hotel began to go up into flames.

Sherringford escaped the fire with only minor injuries, but not Azathoth, who was fatally injured. An irate Sherringford lunged at Watson, accusing him and his friends of having killed his god, a crime for which nothing could atone. Sherlock stepped in to save his best friend, forced to bludgeon his own brother to death using a length of pipe. Shortly before Sherlock delivered the killing blow, a maddened Sherringford delivered his last words: "The horror… the horror!" (PROSE: All-Consuming Fire)

Behind the scenes

 * "Sherrinford" was one of the names Arthur Conan Doyle considered for his protagonist before settling on "Sherlock". first included Sherrinford as Sherlock's eldest brother in the fictional biography.