Lucian Gregory is a dark-red-haired anarchist with a fiery personality, serving as an antagonist and facilitating Syme's infiltration into the anarchist movement. He is characterized by his hatred for society and desire to destroy the world.

Sunday is a large, white-haired figure who paradoxically presides over the Central Anarchist Council and plays a pivotal role in the detectives’ journey. Both authoritative and enigmatic, his presence dominates every scene.

The Secretary, also known as Monday, is the first council member Syme meets, recognizable by his intellectual visage and sinister smile. His identity remains ambiguous until later in the novel.

Gogol is initially depicted with wild brown hair and a Polish accent but is later revealed to have an entirely different appearance. He is the first policeman to be exposed among the council members.

The Marquis de St. Eustache is a distinguished man with a square-cut beard who works undercover as Inspector Ratcliffe. His dual identity is significant to the unfolding intrigue within the anarchist council.

Professor de Worms, while appearing old and frail, is actually a young actor and detective named Wilks utilizing his disguise to penetrate the anarchists’ circle. His disguise contributes to the mystery surrounding the council.

Dr. Bull is a short, clean-shaven man shrouded in secrecy due to his dark spectacles, leaving his eyes hidden. Initially perceived as threatening, he plays a key role in the unfolding assassination plot.

Rosamond Gregory, with gold-red hair, is Lucian Gregory’s calm and motherly sister, offering a stark contrast to her brother’s intense nature. She is the sole female character, embodying maternal and tranquil characteristics.