Frequently, the author surrogate is the same as the main character and/or the protagonist. As an example, the author surrogate may be the one who delivers political diatribe, expressing the author's beliefs at an appropriate time, or expound on the strengths and weakness of other characters, thereby communicating directly the author's opinion on the characters in question.
Most stories have an author surrogate, in that the author is usually capable of pointing to one character (major or minor) whom he or she identifies with to a much greater degree than any other character. This can take the form of a realistic depiction of the author, or a negative (Woody Allen) or positive depiction of the author.
Compare: audience surrogate, autobiographical novel