Symbolism, Imagery, Allegory
[Raskolnikov:] "Yes, that's what it was! I wanted to become a Napoleon, that is why I killed her.... Do you understand now?"
Sonia: "N-no. […] Only speak, speak, I shall understand, I shall understand in myself!" (5.4.113-114)
Remember when Raskolnikov called the sketchy man in the park a "Svidrigaïlov"? Svidrigaïlov, for him, is a symbol of all men who want to abuse young girls. He speaks of Napoleon in the same way, as a symbol, the name not of a man, but of a type of person.
Interestingly, in battle with Napoleon's army, thousands of Russian troops were killed, but Napoleon was eventually forced into retreat. But, before that, he had all of Europe in a state of terror. Imagine that power. Raskolnikov does.
What gets him is that Napoleon had an inexhaustible supply of blood on his hands when he died. Yet, he's celebrated, worshiped, revered. So if Raskolnikov can kill somebody and then be revered (after his death?), he'll be a Napoleon, or something like that.
Even though Raskolnikov explains over and over again how his Napoleon fixation gave him the idea to murder Alyona, the explanations always break down, and he admits it. Like here, after he explained it to Porfiry: "How can they digest it! It's too inartistic. 'A Napoleon creep under an old woman's bed! Ugh, how loathsome!'" (3.6.58).