This is a traditional autobiography, so the author, narrator, and main character are all the same person. Seems obvious, right? Let us explain why it's complicated. See, there's Franklin as author, but he's also the narrator and the main "character" of the story he's writing, which he tells us is true. This raises interesting questions about honesty and integrity in the text. Should we treat it all as true, just because this is what Franklin tells us? Or should we be skeptical?
We also have to think about what Franklin's doing as the author versus how he's describing what happened to him as a character. When Franklin tells us how a real-life, historic event happened, we're taking his word that how he describes it is how it went down, and sometimes we forget whether we're listening to him as author or as narrator/character.
Franklin's also editing the events that happened in his life, and he presents them in a specific way. (For example, he talks a lot about working on being virtuous, but he doesn't talk about how he had one son out of wedlock, and adultery's just not that virtuous.) While this would ordinarily be complicated enough, we could also think about the idea that Franklin considers his life itself as a kind of book. Well, if life's a book, that makes us wonder who the author of that book is – maybe it's God. What does it mean, then, if Franklin's also writing himself as a book?