self-insertion

A brand of fanfiction in which the author inserts himself into the story. In most cases, he has superpowers and/or a Mysterious Past(tm), solves all the characters' problems, saves the day habitually and, of course, has the most desirable female in the show falling for him.

There are SI stories that are not written by 14-year-olds with a self esteem problem and no literary talent, and which therefore don't suck, but they are few and far between.

An example of this (though not following -brazil-'s case) would be in Clive Cussler novels. Cussler usually inserts himself as an extremely minor character. Usually when the main character sees this character he says something along the lines of "You look familiar, what is your name again?" And the character turns out to have the same name as the author.

Done best by Kurt Vonnegut in his book Breakfast of Champions. He reveals himself to the character Kilgore Trout (who is himself already a self insertion of Vonnegut into the book), and proves this by teleporting Trout around the earth, through time, onto the surface of the sun, then back to their starting point without harm.

Then he gets chased off by an angry dog, permanently retracting his testicles in the process.