Palpatine admits to Darth Vader that the Jedi he actually feared most was none other than Jocasta Nu. "Who?" I hear a lot of you of ask. Well, I'm sure most will recall hearing the name at some point. Now that you remember her, let's actually explain who she was.
Originally Answered: What Jedi did Darth Sidious fear the most? Luke Skywalker. Sidious had a vision that Luke could destroy the Sith, and he was concerned. None of the prequel trilogy Jedi frightened him.
As powerful as Darth Sidious may have been, it's easy to forget he actually seemed afraid of Master Yoda. As seen in Revenge of the Sith, Palpatine initially thought he could deal with the aged Jedi Master - and then, when Yoda proved able to counter the Sith Lord's Force lightning, he fled.
When Qui-Gon Jinn showed up on Naboo and threatened to throw a bantha-sized wrench into his plot, Palpatine had to act fast. He dispatched Darth Maul to get rid of the Jedi Master once and for all. Therefore, just like Yoda said, Palpatine's fear led to evil deeds, death and the rise of the dark side.
Emperor Palpatine admitted to fearing Luke Skywalker and even said that if he had him by his side instead of Kylo Ren, he would have won the galaxy.
In the novelization of Revenge of the Sith, we see that Palpatine feels genuine fear during this battle. Not only this but when asked about the fight George Lucas himself has said that Palpatine WAS overcome. This is due to mainly to Mace's fighting style, reflecting the power of Palpatine back at him.
The dark lord revealed
Leaving Palpatine's office, Skywalker quickly went to the Jedi Temple and informed Jedi Master Mace Windu of Palpatine's true identity, though he was greatly conflicted about doing so.
Unfortunately for the galaxy, as Palpatine grew in power the shroud of the dark side fell over the galaxy, diminishing the Jedi's ability to sense the Force. Thus Yoda failed to realize how close to home the Sith really were - until it was far too late.
Aware that the Jedi Order could be destroyed, Windu sought to prevent this outcome by leading a team of fellow Jedi Masters, Kit Fisto, Saesee Tiin, and Agen Kolar, who were among the finest warriors in the Order, to arrest Palpatine, leaving Skywalker behind.
In non-canon material it is said that Palpatine had a number of concubines and never took a wife in fear that he would produce a legitimate heir. One of these non-canon concubines was Roganda Ismaren, a former Jedi who survived Order 66, and lived for a time at Palpatine's side.
That said, Vitiate, sometimes better known as the Sith Emperor, is often thought to have been stronger than Darth Sidious thanks to his mastery of the Dark Side of the force which granted him a ridiculously long life.
Even after his brutal scorching in the fires of Mustafar, sand remained the only natural phenomenon that Vader feared. To him, sand was a reminder that he'd failed to save his mother or Padme from death.
This is particularly clear within the third episode, “Choices,” which focuses on Dooku and Windus' investigation into the death of a Jedi Master. While Dooku is willing to question the Jedi Council's orders, Windu does nothing but serve as an ideological mouthpiece for his superiors.
Giving in to his feelings, Anakin cuts off Mace Windu's hand, giving Palpatine the opportunity to kill him. Anakin regrets this almost instantly, but the thought of Padme was stronger than his remorse This is the moment Anakin officially became Darth Vader and led to serious issues in the Skywalker Saga.
The maverick Jedi Master Qui-Gon Jinn comes before the Jedi High Council, which Windu is a member of, and offers to train Anakin Skywalker, believing that the boy is the Chosen One of Jedi prophecy. Windu and the other Council members decline, deeming Anakin too old and full of fear.
It's the intensity of reflected lightning and the channelling of such raw dark side power that are the catalysts for Palpatine's transformation. Perhaps the face that boils up to the surface is shaped by his dark side corruption, but the lightning is definitely the cause.”
In Palpatine's version of events: Anakin Skywalker accompanied the Jedi Masters into the office, not knowing what they intended. When he realized that they were attempting a coup, Anakin turned on them and bravely defended Palpatine, and managed to kill all four Jedi Masters at the cost of his own life.
Windu eventually gets the better of Palpatine before deflecting his Force Lightning back against him, which appears to twist and melt Palpatine's face as his body begins to smoke, turning him into the grotesque embodiment of the Sith that acts as the final antagonist for both Star Wars: Episode VI - Return of the Jedi ...
Like all Jedi, Mace deeply respects Yoda and regards him as the oldest and wisest Jedi of his time. He always obeys the ancient Jedi Master, but as a senior member of the Jedi Council, he is one of the few who dared to question him, though he rarely does so.
1 Darth Sidious
As well as being a gifted bladesman Sidious' connection to the Dark Side is extremely powerful, granting Sidious the ability to conduct force lightning.