Scott Pilgrim is the central figure. He's a twenty - something guy trying to figure out his life. Ramona Flowers is the love interest. She has a mysterious past and her ex - partners are quite a diverse and strange bunch. Scott's friends, such as Kim Pine, also add depth to the story. They are there to support (or sometimes annoy) Scott as he embarks on his journey to be with Ramona and battle her exes.
Well, Scott Pilgrim is the obvious main character. He's a bit of an aimless young man at the start. Ramona Flowers is very important as she is the focus of Scott's romantic pursuits. Then there are his roommates and friends. Wallace Wells, for example, is Scott's gay roommate who often gives him advice, whether he wants it or not. And of course, the seven exes of Ramona are also major characters in the sense that they create most of the conflict in the story.
Scott Pilgrim was indeed a comic first. It had a dedicated fan base from the comic world before branching out into other entertainment areas. The comic's success paved the way for its expansion into various mediums.