Trope: Author Avatar
Description: Not limited solely to books, the Author Avatar is a version of the creator of a work inserted into the work itself. This can work in a number of different ways. Sometimes the Author Avatar is the narrator, giving opinions on what's going on in the story. Other times, he/she just makes a cameo appearance as a minor character. Every now and then, you get a character who is obviously the creator's favorite and can do no wrong, leading to the dreaded Mary Sue (which yes, can happen in canon works).
Examples: Charlie Brown/Charles Schulz, Dante in the Divine Comedy, Liz Lemon/Tina Fey in 30 Rock
Pros: It's important to have a distinctive voice when writing, so why not use your own? Aspiring writers are frequently told "write what you know", so it makes sense to write it from your own point of view, regardless of whether you're blatant about it or try to camouflage it. I only chose three examples for this post, but there are plenty of others out there. If authors from James Joyce to Stephen King (and everyone in between and on either side) have done it, it can't be a terrible technique, right?
Cons: Make your Author Avatar unrealistic and flawless, and your audience is going to rebel. They'll probably rebel loudly. Somewhere along the way, you're going to have to write a character that isn't a version of yourself. Don't let the Author Avatar become a crutch!
Would/Did I Use It?: No, I have not. When Searching the Skies, my first book, came out, some of my friends wondered if Geneva and I were one and the same. We're not. I promise. Sure, there's probably a little piece of myself in all my characters, and some are more similar to my personality than others, but I have yet to write a character who is just like me or is supposed to be my voice. I wouldn't rule it out completely, but as of right now, I have no plans to put myself in any of my writings.