Who is the Russian that Marlow meets at Kurtz's station? How is he described to readers? How does he contrast with Marlow?

Kurtz's devoted companion, he is an idealistic explorer who has wandered to the Congo on a Dutch ship and has been caught in the web of Kurtz's obsessive ivory hunt. He is so young that it is uncertain whether or not he fully understands what he is doing in Africa. He is more or less attracted to the glamor of adventure. His unwavering support of Kurtz makes him humble and admirable.