Baron Adelbert Gruner is the main antagonist of the Sherlock Holmes story, "The Illustrious Client."
A Austrian Baron he is a shameless philander and a murder, who killed his wife and only got away with his crime due to a legal technicality and a suspicious death of the witnesses (its implied he killed him to).
Now living in England following multiple crimes throughout Europe, Gruner has won the affections of the old General de Merlilles daughter Violet, the two met on a Mediterranean yachting voyage using a series of skillful lies and manipulation, as well as his own good looks, charm and air of mystery and excitement, he has managed to convince her of his innocence in his past crimes, and convinced her to marry him.
A mysterious client contacted Sherlock Holmes through Sir James Damery, aware of Gruner's past Holmes takes on the case, and his first step is confront Gruner. Gruner however is unmoved by Holmes investigation, comparing it to "play a hard with no cards in it". And arrogantly boasts of his own successes, at conditioning Violet to reject anything bad she hears about him. He also ends the meeting with an implied threat, telling the story of a French detective who was investigating him, who was crippled for life after being beaten up by a gang of thugs, a week after investigating Gruner.
However, Holmes, with the help of his friend and informant on the criminal underworld Shinwell Johnson, manages to find a Miss Kitty Winters, who was Gruner's last mistress, a woman who's life was ruined by Gruner and is now bent upon revenge. Its reveled the Baron shamelessly collects women, and keeps reports of this in a book he keeps. Knowing that reading this book in his own hand, will break Gruner's hold over Violet, Holmes formulates a plan to steal it. But first takes Miss Winters to see Violet, to see if this will have any affect. It fails to.
Following his warning however, Gruner hirers to thugs to beat Holmes up. Holmes being a strong man, manages to come out of the fight relatively unharmed, but seeing an opportunity he has the newspapers reports he is seriously wounded and near death, so that Gruner will underestimate him. He also gives instructions to quickly remove Miss Winters in case Gruner tries to have her removed as well.
Several days later, as Gruner is leaving for America and will almost certainly take the incriminating book with him, Holmes is forced to act. He has Watson learn all he can about Chinese poetry in 24 hours, as the Baron has an interest in and is quite the authority on the subject. Then using a genuine piece of Ming poetry has him pretend to be another collector there to sell it to him. While Holmes steals the book.
However Watson is unable to fool Gruner for to long, and confronts him. But before he can do anything, he is alerted by the sound of someone in his back room. Rushing in he's just in time to see Holmes escape out the window. He rushes to the window, only to be doused by vitriol by the vengeful Miss Winters, severely disfiguring his face. Watson stayed on hand till his doctor arrived.
Following this the plan was a success, and shortly afterwards Miss Violet called off the engagement, while Miss Winters was investigated but after hearing the evidence was only given the most minimal sentence for her actions.