In fiction, the term NARRATOR is used for the ostensible author or teller of a story. In first person, the "I" is the NARRATOR. The NARRATOR may be in any of various relations to the events described, ranging from being their center (the protagonist) through various degrees of importance (minor characters) to being merely a witness. A NARRATOR is always present, at least by implication, in any work. A NARRATOR may be reliable or unreliable. If reliable, the reader accepts without serious question the statements of fact and judgment. If unreliable, the reader questions or seeks to qualify the statements of fact and judgment.
The NARRATOR may not always be the main character. In first person point of view, the narrator is most often the main character. However, there are instances where this isn't the case. In Breakfast at Tiffany's (awesome title btw) by Truman Capote, a first-person novel (more like a novella), the narrator is not the main character. The story consists of the narrator's relationship with and observations of the real main character, Holly Golightly (even more awesome character name).
(This post has been inspired by and in some instances, directly quoted from A Handbook to Literature, 8th Edition, by William Harmon and C. Hugh Holman)