The book is written in first person though the "I" is never fully identified. It is a person who has lived beneath the floorboards, listening in on conversations but never participating. This person could be Dostoevsky, though he adds a footnote at the end of his first page advising that the person is actually fictional. Dostoevsky says that the person must exist but as a collection of personalities making up one person—the fictional character of this work. For the sake of continuity, "I" is identified throughout this guide as Dostoevsky.
It's noteworthy that Dostoevsky writes to an audience and that he's fully aware that he's writing to an audience, though he continues to insist otherwise. He throws out objections that the reader is likely to voice at a particular point on many occasions. Dostoevsky also says that he's going to test the theory that it's impossible for a man to be totally honest about certain facts in his life. He plans to include some piece of personal information that he's never shared before as a test of that theory—a sure sign that he's aware of the reader. Then he says that he writes in this form only because it's the easiest way to write and that he would be doing things differently if he were indeed writing for an audience.
Notes from the Underground