A Chagrian with impeccable political skills, Amedda served as the Vice Chair of the Republic Senate in the chancelleries of Finis Valorum and his successor, Sheev Palpatine, who was secretly the Sith Lord Darth Sidious, something that Amedda was privy to knowing.
Yoda knew and probaly told Obi-Wan. Darth Vader knew and possibly Thrawn if the book Outbound Flight is cannon. Also Tarkin might of known since he was friends with Palpatine before he became Emperor. Darth Plagueis.
Mas Amedda was the Vice Chair of the Galactic Senate during Chancellor Valorum's term and Palpatine's term. As Vice Chair to Palpatine, Amedaa would become a close ally to the Chancellor, trusted enough to reveal his true identity as Darth Sidious.
Originally Answered: Did General Grievous know Darth Sidious was Palpatine? No. In the novelization of Revenge of the Sith, he makes several remarks to the effect that he clearly has no qualms about killing “Chancellor” Palpatine , or letting him die as a result of his hostage status.
It's unknown whether he ever told Darth Vader's true identity to his closest advisers; some of these knew Palpatine's identity as a secret Sith, so may have known about Darth Vader as well. It's possible Mas Amedda in particular was in the loop, but that hasn't been confirmed.
How Mas Amedda Reacted to Palpatine being a Sith Lord [Legends]
Did Mas Amedda outrank Vader?
Politically speaking, Mas Amedda is the number 2 rank in the entire Empire, just below Palpatine. Whereas Vader has no actual official rank in the Empire, politically or militarily, at all.
When Senator Palpatine succeeded Valorum as Chancellor, Amedda retained his position under the Republic's new leader. Amedda was one of the few in the galaxy who knew Palpatine was a Sith Lord, and assisted the Chancellor as Speaker of the Senate, helping him manipulate Senators into granting him more and more power.
Indeed he did. Dooku (aka Darth Tyrannus) knew his master's identity. At this point the Jedi thought Dooku was the Sith Master. The kidnapping was planned to reinforce public support for Palpatine while further confusing the Jedi about his true identity.
Maul most likely knew Sidious' double role as Palpatine and Sidious when he served as Palpatine's apprentice. He definitely knew about Palpatine's goal of creating a galactic empire ruled by the Sith. Maul knows that Sidious is the Emperor.
Sidious wasn't scared of Grievous as he served him as a means to an end, rather that he was concerned about what the Kaleesh Cyborg would do if he ever knew about Sidious orchestrating both sides during The Clone Wars.
After the Emperor was killed during the Battle of Endor, Amedda was forced to serve as a figurehead for Fleet Admiral Gallius Rax, the self-styled Counselor to the Empire.
Who is the blue guy that stands next to Palpatine?
That “blue guy” is Mas Amedda, and he ended the Galactic Civil War. He is called Mas Amedda. He was the Vice Chancellor of the Galactic Republic under Vallorum and then Palpatine. He was involved in the plot to soften the image of Vallorum in order for Palpatine to become Supreme Chancellor instead.
Even in the old Star Wars canon, the two had a confrontation, as they met in the comic book Star Wars Tales #9, where Maul pieced together that Anakin was Vader.
A Sith Lord with the ability to cheat death and create life, Plagueis is the enigmatic mentor of Sheev Palpatine / Darth Sidious, who, in accordance to the Sith's Rule of Two, eventually betrays Plagueis by murdering him in his sleep, taking his place as Sith Master.
Sidious revealed to Maul that he did not intend to kill his former apprentice, as he still had use for Maul; it was Sidious' hope that Maul would lead the Sith to Mother Talzin, Maul's mother and the leader of the Nightsisters, so she could be eliminated as a potential threat to the eventual Sith rule of the galaxy.
He was: Darth Tyrannus. His persona as Count Dooku was better suited to his role as leader of the Separatist faction. If he revealed himself as a Sith publicly, rather than just a former Jedi who left the order because of its supposed corruption, that would have damaged his credibility to most of the Separatists.
Plagueis, however, was fully aware of Maul's existence, and supported Sidious's decision to train him. The primary reason for Plagueis's support, despite the violation of the Rule of Two, was that Maul was trained to be expendable.
Studying Jedi Archive records, Dooku based his new weapon design after the curved hilts that were standard during the heyday of Form II lightsaber combat. The curve allowed the hilt to fit better into his hand, allowing for superior finesse and precise blade control.
What we do know is he knew that the clone wars would happen, he says that in the clone wars. This means that he most probably knew about the clones and order 66. He doesn't know about anikin until about a week before order 66.
