Character Arc
William James Moriarty is the heart and engine of the series: a red-haired prodigy of breathtaking intellect whose gentle exterior conceals an unshakable resolve. Born a commoner and orphaned young, he and his brother Louis were taken into the aristocratic Moriarty household, where William witnessed firsthand the casual cruelty the nobility inflicts on those beneath them. That experience crystallizes into a lifelong conviction that Britain's class system is a sickness that must be excised, whatever the cost.
As the secret mastermind known as the Lord of Crime, William choreographs an escalating campaign against the corrupt elite, using murder, manipulation, and elaborate staging as instruments of reform. He is haunted throughout by the price of his methods, insisting that he himself must ultimately be punished for the lives he has taken so that a fairer society can be built on the ashes of the old. His self-appointed martyrdom gives the show its tragic spine.
His arc pivots on the arrival of Sherlock Holmes, the first person clever enough to threaten his plans and, paradoxically, the first to truly see him. Their rivalry blossoms into a profound mutual understanding, complicating William's plan to vanish as the villain history demands. By the finale his crusade collides with his humanity, forcing a reckoning over whether redemption is possible for a man who chose to become a monster for the good of others.