Originally Posted by K_Kinnison
THe whole reason was that when Luke confronted the Cloned Emperor he realized there was no chance in defeating him. SO he became an apprentice, and leader of the combine imperial forces. But they both knew it wouldn't last long since Luke used this time to subvert the powers of he Emperor. The Emperor figured it was a good trade off to end the power of the Jedi.
So Luke pretended to be bad? lol