richest man in the world. Early in the novel, Ryland attempts to hire Poirot and invites him to Rio de Janeiro, allegedly to investigate the goings-on in a big company there. Poirot is offered a fortune and is tempted to accept. He eventually declines and the plot point is no longer elaborated. Presumably Ryland intended to recruit him for the organization. He dies when the hidden base of the Four explodes. He represents the power of wealth. Madame Olivier, a French woman scientist. She is stated to be a famous nuclear physicist and analytical chemist. Poirot suspects that she has kept secret the true extent of her research with nuclear power. He believes that she has "succeeded in liberating atomic energy and harnessing it to her purpose". She is said to have used gamma rays emitted by radium to perfect a lethal weapon. She is a widow. She used to work with her husband, conducting their research in common until his death. She is said to look more like a priestess out of the past than a modern woman. She dies when the hidden base of the Four explodes. She represents scientific research devoted to political goals. Li Chang Yen, the Chinese leader and mastermind of the group, said to have the finest criminal brain ever known. He is an unseen character who never sets foot out of China, but is discussed often by other characters. He controls a "scientific force more powerful than the world has dreamed of". It is said that "the men who loom most largely in the public eye are men of little or no personality. They are marionettes who dance to the wires pulled by a master hand, and that hand is Li Chang Yen's". He is the power behind the throne of the East. He is the embodiment of Yellow Peril. His plots are said to include worldwide unrest, labour disputes in every nation, and revolutions in some of them. Elsewhere it is explained that he is a mandarin and lives in a palace of his own in Peking. He oversees human subject research on coolies, with no regard for the death and suffering of his research subjects. He commits suicide at the end. Claude Darrell, known as the Destroyer. He is an obscure English actor and a master of disguise. He is the chief assassin of the group. He appears with ever-changing faces