Claude Darrell

Claude Darrell, also known as No. 4 and the Destroyer, is the main antagonist of Agatha Christie's The Big Four and the hitman of the titular conspiracy organization. Whilst he is not the leader, Claude is the most recurring member in the novel and poses the greatest direct threat towards Poirot and Hastings than any other people.

He was portrayed by Simon Lowe in Agatha Christie's Poirot.

Overview
Claude Darrell, mostly known as the Destroyer and other aliases, is an obscure English actor and a master of disguise. He is the main antagonist of The Big Four novels despite his number, being the chief assassin of the group and the most active threat to Poirot. He is 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.

In Agatha Christie's Poirot
In Agatha Christie's Poirot, the Big Four's true nature changed drastically, and Claude is the sole antagonist of the book. 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, Claude 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.