John Clay is a fictional character from the short story "The Adventure of the Blue Carbuncle," written by Arthur Conan Doyle. He is portrayed as a cunning and resourceful criminal who steals a valuable gemstone, the Blue Carbuncle. Clay's character embodies the traits of a clever thief, using his intelligence to evade capture. In the story, Clay's actions lead to a series of events that involve Sherlock Holmes, the famous detective. Holmes uses his deductive skills to unravel the mystery surrounding the stolen gem and ultimately confronts Clay, showcasing the classic battle between good and evil in detective fiction.