Apollon, like all the minor characters in the book, is filtered through our not-so-impartial narrator. He's either as much of a jerk as the Underground Man claims, or he's been unfairly made the victim of our narrator's unflinching hate for everyone who breathes and even some who don't. It's hard to think that Apollon is as awful as the Underground Man makes him out to be; how can a servant be superior, pedantic, and condescending? On top of that, the Underground Man seems to hate him for things like reading psalms.On the other hand, though, Apollon does seem like a jerk when Liza shows up, but again we can't be sure that the way his actions are portrayed is how they actually went down.
The interesting question with Apollon is why doesn't the Underground Man just get rid of him? Here's our narrator's explanation: "But at that time I could not get rid of him, it was as though he were chemically combined with my existence. Besides, nothing would have induced him to consent to leave me. I could not live in furnished lodgings: my lodging was my private solitude, my shell, my cave, in which I concealed myself from all mankind, and Apollon seemed to me, for some reason, an integral part of that flat, and for seven years I could not turn him away."
Looking over this, the word "inertia" comes to mind. Apollon is a part of the flat, sure, but more importantly he's part of the routine, the way things are. The Underground Man has a hard time changing anything because his hyper-consciousness prevents him from acting. This is why, he explains, he's bogged down in "inertia" (remember, a resistance to change) – and we can see that playing out here with his servant.