What tools and techniques does the author use to make his premise of another author believable?

Explain why the actual author, William Goldman, creates a fictitious author, S. Morgenstern, for The Princess Bride, trying to pass him off as the real author. How does the narrative device present opportunities for Goldman to take creative liberties with the story? What tools and techniques does the author use to make his premise of another author believable?
essay is to be:
4-5 typed pages (double spaced plus a Works Cited page) Follow the 11-step paragraph format
Documented according to MLA procedures