The manager is a mediocre fellow within the Company, situated at the Central Station. In appearance, he is unremarkable, except for his cold blue eyes and vacuous smile. That expression gives Marlow the willies. (Us too.) He has the tendency to talk a lot and about nothing. The manager is also jealous of Kurtz for his success.
The manager is richly steeped in this sort of "emptiness" imagery. He babbles a lot, but about nothing meaningful and his creepy smile is described as "seal applied on words to make the meaning of the commonest phrase appear absolutely inscrutable." In other words, all his prattle is made to appear profound by his mysterious, but empty, smile. The reason given for his uncommon resistance to disease is that "there was nothing within him." The manager makes the remark that any man who comes to work in the interior "should have no entrails" (much like him). Weirded out yet? The larger implications of this "empty" character are frightening. They imply that the wilderness of the interior has a way of depleting or draining away what makes men human, leaving only a shell of the former self. Sort of like Kurtz, except instead of being replaced by a maniacal, ivory-hungry devil, this guy got replaced by nothing at all.
Since there is nothing within him, everything the manager says and does has no sincerity. All his energy is devoted to keeping up appearances. As Marlow observes, he "originates nothing" because of the void within him. If he cannot create, he can only destroy, which one could say is generally what British imperialists were doing to Africa at the time. We knew this character was here for a reason.