Joseph Conrad's masterful novella "Heart of Darkness" is about a steamboat captain named Marlow who narrates his harrowing trip into the heart or center of the Congo Free State in Africa. Marlow describes his long fascination with the Congo River, a body of water he likens to a "snake" that winds its way through Africa. His interest in the river motivates him to sign on as a captain with a European ivory trading company that is brutally exploiting local people to reap large profits.
The phrase "heart of darkness" has many meanings. Africa was known to Europeans and Americans as "the dark continent" in part because its land and ways were mysterious to outsiders. In addition, the phrase has a pejorative or negative connotation because the "darkness" of Africans was, in the minds of Europeans, associated with darkness in their souls and their supposed inferiority. However, Conrad's point is that the darkness lies not with the Africans but with the brutal European traders.
As Marlow, Conrad's narrator, goes deeper into the heart of Africa, he finds the darkness in the Europeans he encounters, particularly Kurtz, the station master who Marlow is looking for. While other members of the trading company speak of Kurtz in glowing terms, it becomes clear to Marlow that Kurtz has actually become corrupted by the evils of slavery. He writes of Kurtz, "his soul was mad. Being alone in the wilderness, it had looked within itself, and, by heavens! I tell you, it had gone mad." Kurtz has made himself into a type of god worshipped by the locals, and he is clearly charismatic. However, he has used his power to enslave the local people. When Marlow meets him, Kurtz is near death, and, when he perishes, his final words are, "The horror! The horror." With these words, Kurtz tries to repent of his evils. It is clear that slavery and the brutality of European colonialism have corrupted Kurtz and turned his heart to darkness. It is he, not the African people, who has become the embodiment of darkness in the book.