The harlequin is a twenty-five-year-old Russian youth whom Marlow meets as he travels up the Congo River. Marlow calls him the harlequin because he is dressed like the brightly colored jester figure called a harlequin. The harlequin stands on the shore, calling out to Marlow, dressed in clothing covered in patches of blue, red, and yellow. He has blue eyes and a pug nose and looks, to Marlow, "extremely gay [happy] and wonderfully neat."
In talking to him after giving him a pipe, Marlow learns that the harlequin knows Kurtz. He also learns that the youth ended up in the jungle because he ran away from a school in Russia. He has been several times on boats and has ended up in the jungle with no real plan, where has been living for two years. Marlow says of him,
His very existence was improbable, inexplicable, and altogether bewildering. He was an insoluble problem. It was inconceivable how he had existed.
Marlow is taken with the odd and flamboyant figure, saying he admires and envies him for his "glamor," his audacity, and his "pure" spirit of adventure. Most importantly, however, is the harlequin's knowledge of Kurtz. Marlow is astonished to find that the harlequin admires Kurtz and that the natives "adore" him and are ruled by him.
The harlequin describes Kurtz as a dangerous man. He has spent long evenings with him listening to him talk, but Kurtz has also threatened to kill him to get his ivory. He has to be careful of Kurtz's moods. He also says that Kurtz is getting ivory not through trading but through looting and using his gun to intimidate then natives. While Marlow and the manager are talking to the harlequin, they see the ill Kurtz for the first time, carried on a stretcher and surrounded by worshipful natives.