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.
For the most part, no. Palpatine had a rule that anyone who witnessed him using the force had to be eliminated. Notable exceptions were of course Darth Vader as well as the Royal Guards.
The audience never sees the Count openly conspiring with Palpatine (only Sidious) and their conversations never make any overt references that would confirm Dooku was fully clued-in as to his master's grand deception.
But only a few people who [he] allowed to know that Palpatine and Sidious are both one and the same are primarily his apprentices: Darth Maul, Darth Tyrannus/Count Dooku, and his soon to be apprentice Darth Vader/Anakin Skywalker.
DARK SIDE FRIDAY - Did you know Palpatine feared Qui-Gon Jinn? Palpatine was immensely powerful and he could see the future which made him very confident about pretty much anyone who stood against him.
Sidious used Plagueis' methods to transfer his consciousness to a new body after his first demise. During the Battle of Endor in 4 ABY, Sidious was killed by a redeemed Anakin Skywalker, who turned back to the light side of the Force and threw Sidious down a reactor shaft to save his son Luke Skywalker.
Wilhuff Tarkin
Like Vader, Tarkin was one of Palpatine's most trusted followers.
Darth Jar Jar, known to most as Jar Jar Binks, was a Gungan Sith Lord. He survived the Battle of Naboo and became a Representative of Naboo, when he helped to give Darth Sidious emergency powers.
The six-part Disney+ series takes place between the prequel trilogy and the original trilogy, so it makes sense that Emperor Palpatine is not only alive, but thriving. No need to return, because he has nothing to return from—he's recently executed Order 66, and is on top of the galaxy.
In The Rise of Skywalker's novelization, written by Rae Carson, it's revealed that Rey's father is a failed Palpatine clone. He was initially created as a vessel to house the Sith Lord but proved incapable of doing so.
Yoda and Obi-Wan Kenobi battled their way into the Temple to deactivate the signal. There, Yoda discovered evidence that Anakin had fallen to the dark side, and was now a servant of Palpatine. Chancellor Palpatine was, in truth, Darth Sidious, Sith Lord.
The Third Sister Was a Jedi Youngling
The reason why the Third Sister hates Obi-Wan Kenobi so much is because she was a Jedi initiate when Order 66 happened. On that infamous day, Reva was training with her fellow Jedi younglings in the Jedi Temple of Coruscant.
Well, a new Star Wars tie-in has finally answered that question. In The Rise of Skywalker's novelization, we learn that Rey's father was a failed clone of Emperor Palpatine. He was initially created to be a vessel to house Palpatine and his Sith power.
Ultimately, Yoda was forced to flee after coming to the conclusion that he could not possibly defeat Sidious, despite his great ability.
Darth Sidious, publicly known as Sheev Palpatine from Naboo, became the Dark Lord of The Sith after betraying and murdering his Sith Master Darth Plagueis. Sidious was the Dark Lord of the Sith during the last years of the Republic and the rise of the Galactic Empire.
While many Sith Lords are mentioned, only six are detailed in canon: Bane, Plagueis, Sidious, Maul, Tyranus, and Vader.
Realizing that the Sith's greed led to their destruction, Bane created the Rule of Two. The Sith thenceforth consisted of only two Sith Lords at any given time; the master who embodied the power of the dark side, and the apprentice who craved that power.
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.
Mission to Mathas. Padawan Windu was trained in the ways of the Force by Jedi Master Cyslin Myr.
Snoke was a Force-sensitive humanoid genetic strandcast male who ruled the First Order as Supreme Leader during the New Republic Era.
A Sith Lord with the ability to prevent death and create life, Plagueis is the 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.
In 19 BBY, having completed his plan to turn Anakin Skywalker to the dark side of the Force, Darth Sidious claimed his late master Darth Plagueis to have gained the ability to cheat death and to preserve the lives of the ones he loved by influencing midi-chlorians.
Dooku voluntarily left the light side behind and became Darth Sidious' dark side disciple, taking the secret name Darth Tyranus and leading the Separatist army.
Father of Rey
Dathan had a relationship with Miramir, who gave birth to their daughter, Rey. In addition to rejecting Sidious, Dathan married a woman named Miramir, whom he fell in love with. Together, they conceived a child, their daughter Rey, who was born in 15 ABY.