The frame story of Heart of Darkness contains Marlow on a ship with three friends: the unnamed Narrator, an Accountant, and a Lawyer. These characters have little to do with the novel, except for the narrator who serves as an audience surrogate. The Narrator's profession is never specified, so he is a representation of the objective Reader, viewing the story without comment. The Accountant and Lawyer speak occasionally, but not with specificity; it is not known which one speaks and it doesn't matter. In fact, their professions have almost nothing, if not absolutely nothing, to do with the story.
The Lawyer -- the best of old fellows -- had, because of his many years and many virtues, the only cushion on deck, and was lying on the only rug. The Accountant had brought out already a box of dominoes, and was toying architecturally with the bones.
(Conrad, Heart of Darkness, gutenberg.org)
The best relation these characters have to the story is how they are seen; like most of the characters in the story, they have no names, just profession descriptions. Marlow tends to objectify people by their profession or employment; he doesn't care much for names, and even Kurtz's former lover is only "The Intended." In this manner, the mode for recognizing and understanding the characters is set up at the beginning; characters will be identified by their occupation, not by name, because in the jungle, their names don't matter as much as their actions. The individuality of names vanishes under the need for movement; if they stop moving, they die, and are replaced by equally-nameless people. This shows one major theme of the book: outside of civilization, people don't matter; only actions matter, and those actions only matter if they are observed, because otherwise they are as meaningless as an individual name.