Charles Augustus Milverton was a blackmailer.
Milverton extorted money from the families of rape victims and was considered by Sherlock Holmes to be a professional blackmailer. He had a man named Stuart Bloom hold copies of the material, to release in the event of Milverton's incarceration or death.
One of his victims, Anthony Pistone, confronted him and punched him, giving him a cross shaped scar with his ring. Milverton was able to stop Pistone by offering a piece of his blackmailing business.
When Stuart Bloom demanded more money, Milverton ambushed him while he was bathing and stomped his chest repeatedly, drowning him. Since Bloom was too heavy to move, Milverton covered the floors with his cat litter to cover up the stench.
Eventually, Milverton acquired digital recordings made by a serial rapist and began to blackmail the families of the rape victims to keep the tapes secret. One of these victims was Ken Whitman, the father of Eva Whitman, who was Alfredo Llamosa's former sponsor back when he was first trying to get off drugs. Needing to talk to someone about the blackmail, Whitman spoke with Alberto, who put him in touch with Sherlock Holmes in the hope that he could find the blackmailer.
That night, Sherlock tracks Milverton to his home based on the dummy bank accounts used to transfer the money; Holmes speculated that Milverton had such faith in his system that he simply never bothered using more sophisticated methods of covering his tracks. When Milverton leaves his home to buy groceries, Sherlock breaks into his home in an attempt to destroy the scandalous material that is located on Milverton's laptop, but soon discovers a wide variety of material. As Milverton returns home ahead of schedule, Sherlock quickly hides in Milverton's bathroom. As Milverton returns, another person breaks into his home from the backdoor and shoots and kills Milverton. Sherlock is placed in an interesting quandary because if he reveals the death of Milverton then the accomplice would release the information on the internet. However, the subsequent investigation reveals that Pistone was Milverton's new accomplice and sought to take over the blackmail business himself, the investigation concluding with Milverton's tapes being destroyed and Pistone sent to prison for his murder.