First-Person (Central Narrator)
Since this book is written entirely as a diary, Antoine Roquentin is our first-person central narrator. True, we get a short note from the editors of this diary at the beginning of the book. But after that, it's all Antoine all the time.
Sartre achieves some really interesting things by using Antoine as a narrator. For example, he makes us question everything we read by having Antoine condemn his own writing at different points in the diary. We can see this self-criticism when Antoine writes:
How could I have written that pompous, absurd sentence yesterday: "I was alone but I marched like a regiment descending on a city." I do not need to make phrases. I write to bring certain circumstances to light. Beware of literature. I must follow the pen, without looking for words. (13.1-3)
In other words, Antoine wants to record his experiences of the world as objectively as possible, but he struggles with the fact that it's impossible for a single human being to see the world objectively. We are always using words to talk about our experiences, and our words always put some kind of "spin" on our perspective… whether we want them to or not. Antoine wishes he could overcome this limitation of being human, but in the end, he can't.