Why do they call the novel "The Great Gatsby"?

The book is about his reputation and about how everyone sees him. So it isn't so much whether he's great, but that he's a certain kind of person who has a certain lifestyle which is very visible. You can almost say in a wistful tone, "Ah, the Great Gatsby, how he..." and you know he's long dead. 'Great' is like a part of his nickname or a title.