An orphan enduring poverty and class discrimination in late 19th-century Britain, William James Moriarty and his younger biological brother were adopted by Albert James Moriarty. To dismantle the corrupt aristocracy, he murdered Albert's abusive biological brother, assumed the victim's identity, and orchestrated the burning of the family estate, marking his rebirth. He demonstrated exceptional intellect from childhood, self-educating through unauthorized library visits and advising peers and adults. His academic achievements led to becoming a King's Scholar alongside his brothers and securing a mathematics professorship at Durham University by age 24. Publicly, he embodied an elegant, courteous nobleman, renowned for charisma and kindness. Privately, he operated as "the Lord of Crime," masterminding murders of corrupt aristocrats designed as meticulous exposures of societal injustice. His methodologies blended deductive reasoning rivaling Sherlock Holmes with manipulation, stealth, and strategic use of fire as both weapon and symbol of purification. He wielded a sword concealed in a cane, orchestrating crimes as theatrical performances to provoke public awakening against class oppression. Despite his violence, he felt deep compassion for oppression's victims, viewing himself as a "necessary evil" destined for self-sacrifice. Guilt over the bloodshed eroded his mental state, fostering emotional detachment and a death wish by the "Final Problem." His relationship with Sherlock Holmes evolved from calculated manipulation to mutual intellectual respect and profound camaraderie. Recognizing William's inner conflict, Holmes intervened during their Reichenbach Falls confrontation. William survived with severe injuries, including a blinded left eye requiring an eyepatch, and faked his death. Holmes convinced him that atonement required life, not death. Later, he relocated to New York under an alias, working covertly with allies like Billy the Kid. Though physically diminished and psychologically scarred, he embraced anonymous acts of justice to atone. His personality regained aspects of his younger self—greater emotional expressiveness and determination—while retaining the weight of his remorse. His undisclosed biological name symbolizes his enduring identity as a "nameless sacrifice" for societal change.