In Harry Potter and the Goblet of Fire, “Professor Moody" mentioned that he would only be teaching for a year, and only because he owed Dumbledore a favor. What was this favor and what made it so important that it made Moody agree to give up a year of his life to teach DADA?
Here it is from Harry Potter and the Goblet of Fire:
"You'll be Arthur Weasley's son, eh?" Moody said. "Your father got me out of a very tight corner a few days ago.... Yeah, I'm staying just the one year. Special favor to Dumbledore.... One year, and then back to my quiet retirement."
~ Harry Potter and the Goblet of Fire