5 is No Jedi can stop us: Kill all the Jedi masters.
This is for only the four jedi masters you are sent to meet. When you met the ones on Onderon or Nar Shadow, you can choose to kill or talk to them. Choose kill for this achievement. Your choice with the first of these two that you met sets on the path for this achievement. Once you've killed a Jedi master, each other Jedi master will demand to fight you as well.
The exception is the one on Dantoone. No matter what you do, you can't kill him yet. Wait until the endgame, when you have completed the four planets. If you killed the other masters, he will attack you. Killing him will unlock the achievement.