That prolific word count led to fifty novels in the 14 years between 1894 and 1908, with some of the most popular featuring Dr. Nikola. Nikola is an occultist anti-hero in search of immortality and world domination, who uses hypnotic powers and studies witchcraft and the occult. The Nikola series was launched in 1895 as the serial "A Bid for Fortune" in The Windsor Magazine, a rival to The Strand. The series only amounted to five works in all, but Dr. Nikola became almost as popular as Sir Athur Conan Doyle's Professor Moriarty in 1890s Britain.
Nikola is described as dressing in "faultless evening dress, slender, having dark peculiar eyes and dark hair, and white toad-coloured skin." He lives in a bungalow on the Rue de Lafayette in Shanghai (leading some to say the character of Sax Rohmer's Fu Manchu was based on him). John Norris, the host of the Pretty Sinister Books blog, wrote about Stanley L. Woods, who often illustrated the Nikola stories, portraying him in white cravat and fur coat, with his frequent companion, the baleful-eyed black cat Apollyon, perched on Nikola's shoulder.
Dr. Nikola (also known as Dr. Nikola Returns) was a sequel to A Bid for Fortune. In the first book, Nikola tried to obtain a Chinese carved stick said to have almost limitless occult powers. In Dr. Nikola Returns, the doctor continues his pursuit of the powers associated with the Chinese talisman, but enlists the assistance of the penniless but adventurous Wilfred Bruce, who speaks fluent Chinese and also serves as narrator of the tale. Dr. Nikola and Bruce scheme to penetrate the most powerful secret society in China to gain access to a remote Tibetan monastery.
Although Boothby's output was cut short due to his untimely death from influenza at the age of 37, Dr. Nikola lived on in numerous theatrical productions, beginning with Dr. Nikola on the London stage in 1902. In 1909, a three-roll film based on Dr. Nikola was produced by the Danish director Viggo Larsen and was the first novel-based film in Europe long enough to be able to tell the entire story of a novel. A 1935 project that would have starred Boris Karloff as Dr. Nikola never made it to the screen, but Dr. Nikola made a guest-starring appearance in Kim Newman's Anno Dracula graphic novel series from 1992.