How does Marlowe shape our reading of Kurtz in Joseph Conrad's Heart of Darkness?

In Joseph Conrad's Heart of Darkness,
Marlow is new to the world of the Company. While he has experience sailing, he has never
visited the Congo, the "heart of darkness" in Africa. Here is treasure trove in
exporting Africa's valuable resources; for Marlow, who acts as the story's narrator, it
is a place of mystery.

Through Marlow's eyes the reader
sees what Marlow believes Kurtz is, and then what has happened to him. (Ultimately,
Kurtz feels as if a great man has been lost; he becomes sympathetic enough that he
cannot tell Kurtz's fiancée the truth of who and what Kurtz had become—at the story's
end.)

When Marlow fears that Kurtz may be dead as they
travel the river, his disappointment is that he won't be able to
speak to the man. This infers that Marlow believes there would be
value in doing so.

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The point was in his being a gifted creature,
and that of all his gifts the one that stood out preeminently, that carried with it a
sense of real presence, was his ability to talk, his words—the gift of expression, the
bewildering, the illuminating, the most exalted and the most contemptible, the pulsating
stream of light, or the deceitful flow from the heart of an impenetrable
darkness.

Before Marlow even
meets Kurtz, he has a strong desire to learn about the man—his experiences and
knowledge. Marlow's overwhelming desire to meet the man who he has heard so much about
colors our perceptions of Kurtz, presenting him at first as a sympathetic character. By
the end, we need to decide for ourselves what kind of man Kurtz really
was.

Marlow notes:

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Your strength comes in...your power of devotion,
not to yourself, but on an obscure, back-breaking business. And that's difficult enough.
Mind, I am not trying to excuse or even explain—I am trying to account to myself
for—for—Mr. Kurtz—for the shade of Mr.
Kurtz.

Once again, Marlow is
making a case for Kurtz, almost assembling his defense before they meet. As they
approach to make a landing at the Inner Station, Marlow's binoculars find an unusual
sight waiting for them:

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...its first result was to make me throw my head
back as if before a blow. Then I went carefully from post to post with my glass, and I
saw my mistake...food for thought and also for the vultures...They would have been even
more impressive, those heads on the stakes, if their faces had not been turned to the
house.

And...

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...I want you to clearly understand...They only
showed that Mr. Kurtz lacked restraint...that there was something wanting in
him.

These excuses seem out
of place—especially in that Marlow insists..."Mr. Kurtz was no model of mine." Perhaps
his fascination for the Kurtz—the myth of the man—overwhelmed Marlow's good sense.
Marlow believes that the environment helped to ruin
Kurtz:

I think
[the wilderness] had whispered to him things about himself that he did not
know...

Throughout Marlow's
trip to the Inner Station, his thoughts, his imagination, the mystery and mythology that
surround Kurtz, fuel Marlow's desire to meet and understand Kurtz. It is not until they
meet that Marlow understands Kurtz's nature, and his
madness.

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[Kurtz] is revealed upon acquaintance to be a
dying, deranged, and power-mad subjugator of the African natives. Human sacrifices have
been made to him.

We are
unprepared for who Kurtz really is by Marlow's perceptions prior to their meeting.
Marlow struggles with his perceptions and the truth of the man.