Final answer:
The 'Anonymous London killer of 1888' is famously known as Jack the Ripper. Unlike Sherlock Holmes, Dr. Jekyll, and Professor Moriarty, who are all fictional characters, Jack the Ripper was a real and unidentified perpetrator of several murders in London.
Step-by-step explanation:
The 'Anonymous London killer of 1888' is Jack the Ripper. This individual was responsible for a series of gruesome murders in the Whitechapel district of London. The identity of Jack the Ripper has never been conclusively determined, which has added to the mystery and intrigue surrounding these crimes. Other options listed in the question, such as Sherlock Holmes, Dr. Jekyll, and Professor Moriarty, are fictional characters created by authors; Sherlock Holmes and Professor Moriarty by Sir Arthur Conan Doyle, and Dr. Jekyll from Robert Louis Stevenson's novella. These characters are iconic in English literature, but they did not exist in real life.
Additionally, it is important to note that Sherlock Holmes is often misperceived as a real person due to his profound influence on popular culture and the crime-detective genre. But in reality, he was a figment of Sir Arthur Conan Doyle's imagination. The evidence and analysis in the question subtly implied a narrative resembling a detective's deduction, a style famously associated with the Holmes stories.