As part of their planning to take control of the galaxy and the Republic Senate, Darth Plagueis warned his apprentice Sidious that there was one man within the Jedi Order who was a grave threat to their power and rule. Plagueis was extremely fearful of this Jedi becoming the grandmaster of the Order because he did not hold the same dogmatic and rigid beliefs as the current leader Yoda and was open to great change.
This specific Jedi also believed that the Order should become separate from the Republic and become independent peacekeepers, rather than servants of the Chancellor, which would make them a much stronger organisation, something which Plagueis could not accept. On top of all of this, he was probably the most skillful duelist the Jedi Order had seen in many years… His name was Count Dooku. Luckily for Palpatine and Plagueis, Dooku left the Order and was open to be corrupted by the dark side.