Q & As About 'Star Wars': In the Star Wars series, how many people knew (in-universe) that Darth Vader was Anakin Skywalker prior to the revelation in The Empire Strikes Back?

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In the Star Wars series, how many people knew (in-universe) that Darth Vader was Anakin Skywalker prior to the revelation in The Empire Strikes Back?

In-universe, you say?

Well, it goes without saying that Emperor Palpatine knew, since it was he - as Darth Sidious - who dubbed Anakin as “Darth Vader” some 19 years before the events of Star Wars -Episode IV: A New Hope.

As for the rest of the Imperial hierarchy, it’s possible that Vizier Mas Amedda might have known since he was Sheev Palpatine’s trusted confidante and next in line to rule the Empire. However, I can’t be 100% sure, since - from the Sith perspective, the smaller the number of people in the know that both the Emperor and his chief enforcers were Sith Lords, the lesser the chances that the galaxy at large would find out.

Wilhuff Tarkin may have known, or at least suspected, that the Jedi general he had met during the Clone Wars was now “Lord Vader.” In at least two novels by James Luceno - one non-canon, one canonical - the reader is left feeling that Tarkin can put one and together - “Darth Vader” becomes Palpatine’s right-hand Sith apprentice not long after the former Supreme Chancellor’s favorite Jedi, Anakin Skywalker, “died” on Mustafar. In addition, in A New Hope, Tarkin remarks to Vader that “the Jedi are extinct. You, my friend, are all that’s left of their religion.”

The only other Imperial senior officers who might know Anakin Skywalker is Darth Vader are Grand Admiral Thrawn and former Admiral and now Colonel Yularen. In Thrawn’s case, Timothy Zahn’s Thrawn: Alliances shows that the titular Chiss admiral once knew Anakin and collaborated with him on Batuu; several years later, he would return to that far-off planet on another joint mission with the fearsome Vader. As for Yularen, his career has been tied to Vader’s since the Clone Wars, and he isn’t as clumsy or stupid as Admiral Kendal Ozzel.

Other than that, I seriously doubt that any of the other Imperials we saw in the Original Trilogy knew Anakin Skywalker had been turned to the Dark Side and was now “Lord Vader.”

On the Rebel side:

Obi-Wan Kenobi and Yoda knew, for sure, although in Dark Lord: The Rise of Darth Vader, Obi-Wan is unaware that his former apprentice survived their duel on Mustafar until he sees, purely by chance, a HoloNet newscast in which Darth Vader is briefly mentioned and shown. Yoda knows, though, but because he is on Dagobah and can’t use the Force to communicate with “Ben Kenobi,” he keeps this to himself.

(Canonically speaking, it’s possible that Qui-Gon Jinn’s Force ghost tells Obi-Wan that Anakin is Darth Vader, since Dark Lord, as good as it is, was not added to canon after 2014.)

Bail Organa probably knows although I can’t be 100% certain. I do know, though, that he knew that the Skywalker Twins had to be hidden from Emperor Palpatine, Vader or no Vader.

Ben (Obi-Wan) might have insinuated something to Owen and Beru Lars; this would explain Uncle Owen’s reluctance to let Luke apply to the Imperial Academy, as well as his comment to Beru that he’s afraid of his step-nephew having too much of his father in him.
Other than those personages, I think that no one, not even Mon Mothma, knows the truth about Vader’s ID.