In A New Hope, Grand Moff Tarkin and Vader exchange the following words:
VADER Don't underestimate the Force.
TARKIN: The Jedi are extinct. Their fire has gone out of the universe. You, my friend, are all that's left of their religion.
Did Tarkin know that Vader was once
the Jedi Anakin Skywalker?
Or had "Jedi" become a catch-all term for Force users, good or evil, by this point in time?
According to the SW novel "Tarkin", he had very (very) strong suspicions but he kept them largely to himself:
Later, observing the rapport the Dark Lord shared with the stormtroopers who supported him, and the technique he displayed in wielding his crimson lightsaber, Tarkin grew more and more convinced that his suspicions were right. Vader might very well be Jedi Knight Anakin Skywalker, whom Tarkin had fought beside during the Clone Wars, and for whom he had developed a grudging appreciation.
[later]
Sidious assumed that Tarkin had puzzled out that Vader had once been Anakin Skywalker, under whom Tarkin had served during the war. Tarkin may also have determined that Vader was a Sith. If so, it followed that he accepted that Sidious was Vader’s dark side Master. But Tarkin’s intuitions were important only in the sense that he never revealed them and never allowed them to interfere with his own ambitions.
He made a few half-hearted attempts to confirm whether it was Anakin behind the mask, but didn't push the issue:
“If we aren’t willing to do whatever is required,” he said finally, “then we risk losing what we have been mandated to protect.”
The remark paraphrased something Skywalker had said to him following the Citadel rescue. But it got no reaction from Vader beyond his saying, “You misunderstand, Governor. As I said, we need to gather all of them in our net.”
