Marlow is a thirty-two-year-old sailor who has always lived at sea. The novel's narrator presents Marlow as "a meditating Buddha" because his experiences in the Congo have made him introspective and to a certain degree philosophic and wise. As a young man, Marlow wished to explore the "blank places" on the map because he longed for adventure; his journey up the Congo, however, proves to be much more than a thrilling episode. Instead, his experiences there teach Marlow about the "heart of darkness" found in all men: Many (like himself) suppress these evil urges, while others (like Kurtz) succumb to them.
Marlow's chief qualities are his curiosity and skepticism. Never easily satisfied with others' seemingly innocent remarks such as those made by the Manager and Brickmaker, Marlow constantly attempts to sift through the obscurities of what others tell him (such as when his aunt speaks to him of "weaning those ignorant millions from their horrid ways"). However, Marlow is no crusader for Truth. He lies to Kurtz's Intended to save her from a broken heart and ultimately returns to Europe and his home, despite his having been convinced by the Company and Kurtz that civilization is, ultimately, a lie and an institution humans have created to channel their desires for power.
As Heart of Darkness progresses, Marlow becomes increasingly sensitive to his surroundings and the "darkness" that they may embody or hide. When he visits the Company's headquarters, for example, he is slightly alarmed by the doctor's comments and puzzled by the two women knitting black wool. When he arrives at the Outer Station, however, he is shocked at the amount of waste and disregard for life he sees there. By the end of the novel, Marlow is almost unable to reintegrate himself into European society, having become convinced of the lies and "surface-truths" that sustain it. He tells his story to the men aboard the Nellie to share with them what he has learned about the darkness of the human heart — and the things of which that darkness is capable.