Big Four

"There are people, not scaremongers, who know what they are talking about, and they say that there is a force behind the scenes […] A force which aims at nothing less than the disintegration of civilization. In Russia, you know, there were many signs that Lenin and Trotsky were mere puppets whose every action was dictated by another's brain."

- A victim's description of the Big Four

The Big Four is the titular main antagonistic faction of Agatha Christie's The Big Four and featured in its adaptation within the 13th and final season of Agatha Christie's Poirot. It is a multiethnic gang of four persons working towards world domination, and is assisted by criminals and other agents, including Countess Vera Rosakoff.

Overview
The Big Four members are led by Li Chang Yen and followed by Abe Ryland, Madame Olivier and Claude Darrell. a secret hideaway in a quarry of the Dolomites, owned by an Italian company which is a front company for Ryland. The quarry conceals a vast subterranean base, named Felsenlabyrinth, hollowed out in the heart of the mountain. From there, they use wireless communications to transfer orders to thousands of their followers across many countries.

Members

 * 1) Li Chang Yen (leader; in China): Li Chang Yen is the unseen main antagonist of The Big Four novel. He is a cruel, greedy and uncaring Chinese warlord in Beijing and the enigmatic leader of the Big Four, only being mentioned and discussed by other chracthers. He is driven by his own lust for power and the need to establish his personal supremacy. He commits suicide at the end.
 * 2) Abe Ryland: Abe Ryland, the so-called American Soap King, is an industrialist stated to be richer than John D. Rockefeller and being the 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. He was portrayed by James Carroll Jordan in Agatha Christie's Poirot.
 * 3) Madame Régine Olivier (in France): Mme. Olivier is a French woman scientist, who is stated to be a famous nuclear physicist and analytical chemist that even exceeds the achivements of Pierre and Marie Curie. She represents scientific research devoted to political goals. Poirot suspects that she has kept secret the true extent of her research with nuclear power, believing she was using her research for her very own purpose. She dies when the hidden base of the Four explodes. She was portrayed by Patricia Hodge in Agatha Christie's Poirot.
 * 4) Claude Darrell (in England): Claude Darrell, known as the Destroyer, is an obscure English actor and a master of disguise. He is the secondary antagonist of The Big Four novels despite his number, being the chief assassin of the group, said to have the finest criminal brain ever known. He appears with ever-changing faces and multiple identities throughout the novel. He can totally transform his physical appearance and his persona. He dies when the hidden base of the Four explodes. He was portrayed by Simon Lowe in Agatha Christie's Poirot, where he is revealed to be the true main antagonist instead of the secondary antagonist like that in the novel.

In TV series
In Agatha Christie's Poirot, the intepretation of the Big Four is drastically different to that in the novels, with the drastical change of its nature as well as the omission of its supporters, including the Countess, who would later make her appearance in the episode of Labours of Hercule instead.

The most significant changes involve the villains themselves. In the novel, all four members of the Big Four are indeed guilty of their crimes, although they live separate lives. In the adaptation, Olivier and Ryland are stalwarts of a Peace Party founded by Li Chang Yen, who is a pacifist rather than a dissident. Olivier and Ryland are each connected to one of the murders, and quickly vanish when suspicion is cast upon them. It is revealed at the end, however, that Li Chang Yen, Olivier and Ryland are all innocent, and were deliberately framed by the sole villain, Claud Darrell.

Darrell's real name here was revealed to be Albert Whalley, who was a brilliant but unhinged actor who staged the entire conspiracy, while desiring to attract the admiration of Flossie Monro, who became an unrequited lover whom he showers with anonymous gifts and cards expressing his love for her.

Unlike in the novel, the climactic showdown does not take place in an elaborate headquarters within a mountain, but in the old repertory theatre where Darrell and Flossie had acted as young adults. There is no deadly explosion, either. Although Darrell attempted to set off dynamite, Poirot reminded Darrell that he cannot kill Flossie. Poirot then persuaded him to dismantle the explosive. Instead, Claude went into a fiery rage and tried to shoot Poirot, but he was killed in time by the journalist Lawrence Boswell Tysoe (an original character not in the novel), who drops a safety curtain on him.

After Darrell's death, the truth was revealed to the public by Olivier and Ryland, who were rescued by Poirot. The Big Four was declared to be fictional with Li Chang Yen (in absentia), Olivier and Ryland had their fame and honor restored. Soon, they continued their work as Peace Party advocates.

Trivia

 * The members comprise typical ethnic and national stereotypes of 1920s British fiction, and their villainy and skills (except Darrell) are unrealistically exaggrated, something that was often criticized by critics and fans alike. Darrell, however, is often considered to be the most realistic member of the group.
 * Li Chang Yen is often considered to be a symbolization of English people's fear over Orientalism at the time, possibly with the character being an echo of the infamous Fu Manchu.
 * David Suchet, who played Poirot for ITV from 1989 to 2013, had a different suggestion as to the origins of the Big Four. He found them to be an evil counterpart of The Four Just Men series by Edgar Wallace. He agrees, however, that Li Chang Yen was inspired by Fu Manchu.
 * Li Chang Yen made no appearance in either novels or TV series.
 * After the release of the TV adaptation of the novel, some audience who watched it had been joking that the real Big Four refers to the original main characters of the Agatha Christie's Poirot series; Poirot, Hastings, Inspector Japp and Ms. Lemon, who all united after more than twenty years of departure.