Very few people knew that Darth Vader and Anakin Skywalker were the same person up to his death in 5 ABY. Imperials who knew in the current canon: Sidious (emperor), Grand Moff Tarkin, all or most of the Inquisitors, Grand Admiral Thrawn, various clones in the early empire.
Palpatine led Anakin Skywalker to the dark side and gave him the name of Darth Vader. The Emperor always knew the truth, and seems to have been the one who decided it should remain a closely guarded secret.
Though it sounds like he thinks Anakin is dead, he could also be viewing it as Obi-Wan does, where he believes Anakin died when Darth Vader was created. There's a hint that Owen knows Anakin was Darth Vader by the time of A New Hope.
And while his warnings don't work, at the very least, it shows that Maul became aware of Anakin and what he would soon become. With the rise of the Empire, it's likely Maul caught on to Vader's existence pretty quickly.
R2-D2 was present when Padmé gave birth to Leia and Luke, so he knew Luke was Anakin's son – but what he didn't know was that Anakin became Darth Vader. In addition to that, Anakin's fall was surely a painful event in R2-D2's life, one that he definitely wouldn't like to remember or even talk about.
Return of the Jedi establishes that Yoda was aware that Anakin Skywalker had fallen to the dark side and become Darth Vader. When questioned by Luke Skywalker, he confided that Anakin was Darth Vader. Later, Obi-Wan Kenobi's Force ghost confirmed that Anakin had indeed fallen to the dark side and become Darth Vader.
At first, Ahsoka has no idea that Anakin Skywalker and Darth Vader are one and the same. She discovers the truth in Star Wars Rebels when she encounters the Sith Lord in a space battle. What she senses is so shocking to her that she passes out.
According to The Force Awakens: Rey's Story, Rey was reading Ren's mind when she talked about Vader. There's no particular indication that she knows who Darth Vader is or how powerful he was, other than what she's pulled out of Ren's thoughts.
But before the battle for Coruscant, they had to split up and Rex went with Ahsoka to Mandalore, and Anakin went to Coruscant. After that, Anakin and Rex never saw each other again.
Rex was 100 percent loyal to Anakin and was his truest friend out in the field. Anakin had to hide so much of himself from other Jedi, but he could be completely open with Rex, and he knew that Rex would never betray him.
Rex is a clone trooper of the Grand Army of the Republic, cloned from the Mandalorian bounty hunter Jango Fett, and serves the Galactic Republic under the command of Jedi General Anakin Skywalker and Jedi Commander Ahsoka Tano.
In the year 3 ABY, Fett saved Vader's life from an assassination attempt. In the aftermath of the battle, Vader revealed to Fett his true identity: Anakin Skywalker, and his past with the Jedi Order. It was here where Fett learned of the fate of Mace Windu, and how Vader had killed him.
Some time after this quest Cal was rifted into the Multiverse Merged universe where he met Luke Skywalker and formed a New Jedi Order with him. Although recent hardships have strained their relationship, Cal and Luke are still trying to restore the Order, now much better than it was before.
The sequence calls back to a similar scene in Revenge of the Sith, when Bail Organa orders Threepio's memory be erased to prevent him from sharing information about Anakin Skywalker's fall to the dark side.
C3PO was clearly created from some sort of kit or existing prototype since every protocol droid aside from coloring looks the same. He didn't recognize him because again, they all look the same & it was decades until he saw him again. There was no reason to believe he or R2 even existed anymore.
Maybe R2-D2 didn't know Darth Vader was Luke's father because he didn't see Palpatine christening him Vader, or maybe he believed Anakin was dead because even Obi-Wan didn't know Anakin was alive.
Leia's Force abilities and her lack of awareness of her true identity also contributed to Vader's inability to sense their familial connection. Vader's denial of Anakin Skywalker's legacy and his fear of getting hurt again prevented him from realizing the truth about his children until later in the original trilogy.
Darth Vader didn't learn he had a daughter until Return of the Jedi, when he stood before Emperor Palpatine. The Emperor's power probed Luke's mind, attempting to goad him to fall to the dark side, and he discovered Leia's existence. "Sister," the Emperor taunted.
Yes. In the book 'Tatooine Ghost', Leia learns of Anakin's life prior to his evolution into the Darth Vader personae. This revelation leads her to forgive him. She even named her third child in memory of her father.
