Before becoming iconic frontman for KISS, Gene Simmons used to teach! So did Billy Crystal, Sting, and Stephen King.
An awesome article from Mental Floss names 15 notable actors, writers, and other public figures who were teachers before they were famous.
For anyone not familiar with the highly addictive Mental Floss, it's a bimonthly magazine "where knowledge junkies get their fix."
URL: http://www.mentalfloss.com/blogs/archives/33288