The Sith Emperor has mastered the dark side's power to become the most dominating Force-user the galaxy has ever seen. His corrupting influence is so complete that none can stand in his presence without succumbing to fear, anger and hatred. The Emperor can wither and ruin even the strongest Jedi's connection to the light side.
Jedi Master Tol Braga's strike team was not the first group to succumb to the Sith leader's oppressive influence. Hundreds of years ago, the Jedi Revan and Malak discovered Dromund Kaas and confronted the Emperor. They fell to the dark side and returned to Republic space as Sith Lords. Since then, dozens more Jedi have followed the same path into evil.