Marlow acts as the reader's moral compass, observing many cruel, shocking, and repulsive sights and witnessing acts of stupidity and moral degradation. His reactions to all he experiences and the judgments he makes provide the moral framework of the novel. The reader's view of Kurtz is shaped by Marlow's relationship with him and by Marlow's final assessment.
Kurtz is presented as the greatest of the ivory traders, the agent who sends more ivory out of the interior than anyone else. Marlow describes Kurtz' appearance in a startling image: "death carved out of old ivory." Marlow associates Kurtz with death, strongly influencing the reader's emotional reaction to Kurtz.
Marlow's narrative detailing the life Kurtz lives at his inner station repulses the reader, just as Marlow is repulsed. Exercising power over the natives and constructing his fence of heads, Kurtz also engages in unspeakable, degrading rites in the jungle. Kurtz becomes a satanic figure, a devil; Marlow associates him with the powers of darkness through numerous instances of devil imagery. Kurtz has "kicked himself loose of the earth" and lives in "impenetrable darkness." He exalts himself: "My Intended, my ivory, my station, my river . . . ." It is this love of self that leads to his victimizing others.
In dealing with Kurtz, however, even Marlow is not completely invulnerable to his power. He begins to identify with Kurtz and merges with him psychologically in the final confrontation in the jungle at night; the jungle drums merge with Marlow's own heartbeat so that he cannot distinguish between them. When Kurtz "rises before him like . . . a night shadow," Marlow faces a moment of truth. He must choose. He can join Kurtz in degradation, abandon him, or overpower him and bring him out of the jungle. For Marlow to have been brought to such a moral crisis emphasizes the power of Kurtz' being: Kurtz is evil itself.
However, the reader's assessment of Kurtz is not final yet, because Marlow's relationship with him continues to be dynamic. After dragging Kurtz out of the jungle and back to the ship, Marlow continues to interact with him. He rejects Kurtz' evil, but he does not reject him as a man. Marlow attends to Kurtz, even comforting him as he lies dying. Marlow acts with compassion and human charity, prompting the reader to see Kurtz as a desperate, broken human soul. With Kurtz' last words, "the horror, the horror," he reasserts his own humanity, and mortality. Marlow's experience with the dying man adds another dimension to Kurtz' character.