According to the Los Angeles Times, Hopper said in an internal email, "The time has come for me to move on from the company and set my sights on new horizons."
Hopper joined Disney in 1991 before being appointed head of the games group in 2002. He was instrumental in the 2007 acquisition of Warren Spector's Junction Point Studios, the developer of Epic Mickey, in addition to Disney Interactive Studios' general foray into non-Disney-brand titles, including Black Rock Studio's Pure and Split/Second racing games. Of course, with Playdom exec John Pleasants now running the show, there are going to be some changes around Disney's games department -- no matter how epic Mickey's adventure proves to be at retail.
[Pictured: Hopper (with Epic Mickey ears); original photo credit: Disney Interactive Studios]