Kurtz is Africa's Satan, whose forbidden fruit is ivory, drawing him away from the rules of civilization and creating a monster that feeds on fulfilling that one job, no matter the consequences.
He presents himself as a god to the natives, who are awed by Kurtz's magnificence and become his devoted followers, his own fallen angels.
There, in the deepest pits of the jungle, those demonic and primitive people and their god partake in hellish rituals, taking all of the ivory they want without hesitation, living as they please
“He is an emissary of pity, and science, and progress...We want...for the guidance of the cause entrusted to us by Europe...higher intelligence...a singleness of purpose...he comes here, a special being” pg.83
Kurtz originally comes as a deliverer, sent to guide and further the cause, to the “good news” of Western colonialism (much like Jesus’ apostle/ Angel Gabriel). Kurtz in the beginning acts as a voice crying in the wilderness and is to make every crooked place straight, every low place high, and every backward, non-western place western for the glory of the colonialist cause. But that was the early Kurtz, the one we know only through descriptions by others. The Kurtz who we first meet in the text through Marlow’s eyes is far different character. He has taken on a demonic aspect.
"You should have heard him say, 'My ivory.' Oh, yes, I heard him. 'My Intended, my ivory,...