When Marlow meets the Russian in the jungle at the Inner Station, not far from where Kurtz is, we learn a great deal about the mysterious Kurtz, the most successful agent for the Company.
Throughout Conrad's Heart of Darkness," different characters speak of Kurtz to Marlow—the steamship captain sent to bring him home, who is totally unfamiliar with Kurtz. Some of the men Marlow speaks with are extremely jealous. Recall the brickmaker (who had no materials to make bricks)—he had hoped to have a management position with the Company until Kurtz showed up and became so outrageously successful, shattering hopes for advancement for him—and other agents.
'...and so HE comes here, a special being...Today he is chief of the best station, next year he will be assistant-manager, two years more and . . . but I dare-say you know what he will be in two years' time...
`When Mr. Kurtz,' I continued, severely, `is General Manager, you won't have the opportunity.'
Other Company employees, the uncle and his nephew that Marlow overhears who so resent Kurtz would not mind at all if he were somehow dead at the Inner Station.
One that greatly admires Kurtz is the Russian who has followed Kurtz for quite a long time. He has nursed him back to health on two occasions, was forced to give Kurtz his ivory (at gunpoint—Kurtz threatened to kill him), and has even had to remove himself from Kurtz's company on occasion to remain safe from Kurtz's fury. Still he greatly admires Kurtz. It is the Russian who explains how the natives feel about Kurtz...and it seems the Russian, for some "crazy" reason, feels the same.
There may be some foreshadowing in this segment of the exchange between Marlow and the Russian:
`But he had no goods to trade with by that time,' I objected. `There's a good lot of cartridges left even yet,' [the Russian] answered, looking away.
Marlow can't understand how Kurtz could make progress with the natives, having nothing left to trade or barter with. However, the Russian notes that there were "...a good lot of cartridges left even yet." The word "yet" would indicate that even after an extended period of time...or an extended use of supplies, there were still "cartridges" (bullets) left. My sense is that many have already been used, but an impressive amount still remains.
`They adored him,' he said. The tone of these words was so extraordinary that I looked at him searchingly. It was curious to see his mingled eagerness and reluctance to speak of Kurtz. The man filled his life, occupied his thoughts, swayed his emotions. `What can you expect?' he burst out; `he came to them with thunder and lightning, you know-- and they had never seen anything like it--and very terrible.'
The "thunder and lightning" (items of "modern civilization") the Russian refers to makes me think that Kurtz used gunfire to impress the natives. They don't seem to hate him at all--they adore him--so he must have demonstrated the power of the weapons, rather than shooting natives. That cartridges remain could infer that he didn't need to use a great many discharges to impress the Africans. And in believing that he was some kind of a god, the natives "adored" him —and ultimately bewail his removal when Marlow takes him, even though he was obviously crazy.
While the Belgians use deception to make the world believe they are in the Congo in order to help the natives, Kurtz uses this deception to ensure the natives' belief that he is some kind of god.