Quote 136
"One day he [the accountant] remarked, without lifting his head, 'In the interior you will no doubt meet Mr. Kurtz.' On my asking who Mr. Kurtz was, he said he was a first-class agent; and seeing my disappointment at this information, he added slowly, laying down his pen, 'He is a very remarkable person.' Further questions elicited from him that Mr. Kurtz was at present in charge of a trading-post, a very important one, in the true ivory-country, at 'the very bottom of there. Sends in as much ivory as all the others put together […].'" (1.46)
Marlow wasn't too interested in Kurtz at first, but he's starting to get curious. As the details pile up—he's a first-class agent, he's a remarkable person, he sends in quantities of ivory—our hero can't help wanting to, um, explore.
Quote 137
"I had plenty of time for meditation, and now and then I would give some thought to Kurtz. I wasn't very interested in him. No. Still, I was curious to see whether this man, who had come out equipped with moral ideas of some sort, would climb to the top after all and how he would set about his work when there." (1.74)
Despite himself, Marlow becomes more and more curious about this faceless figure of Kurtz. From the brickmaker's description of him, Marlow assumes that Kurtz came out "equipped with moral ideas of some sort," probably the sort that try to justify imperialism. When compared to the godlessness of the crew surrounding Marlow, Kurtz seems like a good alternative.
Quote 138
"Where the pilgrims imagined it crawled to I don't know. To some place where they expected to get something. I bet! For me it crawled towards Kurtz—exclusively […]." (2.7)
This has quickly stopped being curiosity and become obsession: Marlow doesn't see the wilderness as his destination anymore, but just Kurtz. (Or are they really that different?)