The First Time
In The Incredible Hulk #4, Bruce Banner developed a gamma ray machine that could turn him from Hulk to his normal self. While the machine cured him permanently, Banner decided that Hulk was needed at times. He continued to use the machine to flip and reverse when he transformed. He ended up liking being in the form. In Incredible Hulk #6, Banner finally used the machine for the last time, with Banner vowing to never become the Hulk again.