Aside from Professor Moriarty, Sherlock Holmes has encountered several other recurring adversaries and antagonists in the original stories written by Sir Arthur Conan Doyle. Some of these adversaries include:
Colonel Sebastian Moran: Colonel Moran is a skilled marksman and a henchman of Professor Moriarty. He plays a significant role in "The Adventure of the Empty House" and is responsible for an attempted assassination of Holmes.
Charles Augustus Milverton: Milverton is a blackmailer who preys on the secrets of the rich and powerful. Holmes faces him in "The Adventure of Charles Augustus Milverton."
Irene Adler: Although not a traditional adversary, Irene Adler appears in "A Scandal in Bohemia" as "the woman" who outwits Sherlock Holmes. She is a former opera singer and a romantic interest for Holmes.
Baron Gruner: Baron Gruner is a ruthless and abusive nobleman who appears in "The Adventure of the Illustrious Client." He is involved in blackmail and murder.
Jonathan Small: Jonathan Small is a key figure in "The Sign of the Four." He is a member of a treasure-hunting expedition that turns to crime, leading to murder and intrigue.
John Clay: John Clay is a master criminal known as "The Red-Headed League" for his involvement in a bizarre bank robbery scheme.
Charles Augustus Milverton: Milverton is a blackmailer who preys on the secrets of the rich and powerful. Holmes faces him in "The Adventure of Charles Augustus Milverton."