Who is the man at the third station (called the Inner Station) in Heart of Darkness, by Joseph Conrad?

In Joseph Conrad's novel, Heart of
Darkness, Marlow, while sitting on the ship called the Nellie, tells his tale
of a trip he took into the heart of Africa. He tells his story to several men:
one is the Director of Companies; one is a lawyer; another is an
accountant; lastly, there is an unnamed man who is the narrator,
recounting Marlow's tale.

Marlow recalls that he has been
hired by the Company to captain a ship that will venture into the Congo and ultimately
retrieve Mr. Kurtz and return with him to England.

The
first station is called the Lower Station. Upon arriving, Marlow is distressed to see
how the natives have been enslaved, how they are beaten and starving, working under
white Company men who act as their guards. For Marlow it is a "vision of hell." There
seems to be pandemonium everywhere: nothing seems to make sense—there are "loads of
rusting ancient wreckage everywhere," and Marlow can seen an outcropping being blown up
for no logical reason.

Marlow's trip continues. The second
stop is the Central Station. It is here that Marlow is supposed to take over the ship he
is to captain, however, it is underwater. It takes quite a while to make the vessel fit
for navigation up the river. In fact, parts that he orders and waits weeks for seem to
mysteriously never arrive from the Lower Station. It seems someone does not want him to
complete his task. The two men that Marlow spends the most time with here are the
manager and the brickmaker. The foreman, however, is helpful in getting the rivets
Marlow needs to finish fixing his ship.

Ultimately, Marlow
and his ship get underway, and after attacks by natives, and the loss of one of his men,
Marlow makes it to the Inner Station, where Kurtz is: he has become something of a god
to the people there, and it seems that Kurtz has gone mad. It appears that it may be
impossible to remove Kurtz, especially as the natives do not want him to leave, but
eventually, Marlow is successful in getting Kurtz on board, and getting the ship
underway.