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.
C3PO, no. His memory was wiped at the end of Revenge of the Sith. A blabbermouth like him can't be trusted with sensitive information. R2-D2, we don't know.
C-3P0's memory was wiped at the end of Episode III so if he wasn't told he had no idea that his maker was the future Darth Vader. R2-D2 remembers it all and if I had to guess he is quiet sad about Anakin's turn to the dark side.
In fact, R2 didn't witness Anakin and Obi-Wan's duel, but he returned to the ship and left the place with the latter, presumably with the knowledge that his former master isn't alive anymore. So, essentially, the droid had no idea that Darth Vader is, in fact, Anakin Skywalker.
By the time Palpers came to rescue Vader, Obi Wan had already taken R2 with him when he left to get Padme to medical treatment. He then gave both R2-D2 and C-3PO to Senator Organa, who in turn gave them to his ship captain, Captain Antilles, along with an order to wipe the memory of the overly chatty C-3PO.
Threepio had his memory wiped at the end of Revenge of the Sith. He doesn't even know Anakin was Anakin.
After the battle, R2-D2 and C-3PO were the sole witnesses to the marriage of Anakin Skywalker and Padmé Amidala in Lake Country. After this Padmé gave ownership of R2 to Anakin while she kept 3PO.
Such cycles of fate no longer surprised the nine-hundred-year-old Jedi. So there you have it. Yoda and R2D2 knew each other and the galaxy is even a smaller world than we think.
When R2D2 was missing in action, Anakin went to great lengths to rescue him, even distrusting his replacement droid, which turned up to be a mole planted by General Grievous. R2 was on Mustafar when Anakin became Vader. That, perhaps, explains that he doesn't try to reacquire him.
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.
Perhaps, the old creature simply forgot. Late in the film, Darth Vader does not recognize C-3PO who is in Cloud City with Han Solo, Chewbacca, and Leia. Although C-3PO is not completely assembled in the scene, he is definitely visible to Vader.
However, Leia's strong-mindedness during Vader's probe denied him the opportunity to discover she was his daughter. That serves to justify Vader's lack of awareness of his connection to Leia, although, perhaps, not as satisfyingly as if Lucas had planned for the relationship from the beginning.
Vader relies on the complex life support system of his suit to survive and it happens to be very vulnerable to electrical discharges. So, if Vader ever had unleashed Force lightning, there's a good chance it would've caused his suit to short circuit, thus, killing him.
The base assumption of why Obi-Wan doesn't remember R2-D2 -- in light of the prequels -- is that Obi-Wan is feigning ignorance in A New Hope to downplay the importance of the droid's arrival.
However, R2-D2's memory is not wiped; as a result, R2-D2 is the only surviving character at the end of the saga who knows the entire story of the Skywalker family. Both R2-D2 and C-3PO end up in the possession of Captain Raymus Antilles (Rohan Nichol) onboard the Tantive IV.
R2 doesn't know it. It's as simple as that. He isn't present on Mustafar (he flies with Anakin but is ordered to stay at the ship. He isn't present while the slaughtering of the seperatists or the fight of Anakin/Obi-Wan.), differently to Obi-Wan and C-3PO.
If he were to take his mask off, the Sith Lord would soon suffocate. So it's the most crucial part of his armor. He can only breathe without the need for his mask when he is in one of his meditation chambers seen in The Empire Strikes Back.
Throughout her encounters with Kenobi in the series, he refers to himself as Ben. The most straightforward explanation would be that Leia knows the person who rescued her is Ben, and never connected the dots that Ben is actually Obi-Wan.
The two droids were dumped back on the streets, their memories wiped of the incident. Unlike R2-D2, Threepio's mind is wiped of all memories after the birth of Luke and Leia.
R2-D2, the indomitable droid and mainstay of the Star Wars series, may be responsible for one more incredible feat: saving Grogu.
Other Characters That Can Understand Droids In Star Wars
Obi-Wan Kenobi was another human who could speak Binary, as well as Anakin, who shared the strongest relationship with R2-D2, as seen in the prequel trilogy and Star Wars: The Clone Wars.
This meant that he would be able to keep the amount of casualties to a minimum. Therefore, he stored the lightsaber inside R2 to force himself to only use it when it was necessary.
What Padmé knew about Anakin's previous dark deeds. Padmé was well aware that Anakin had committed dark crimes that would've started his fall to the dark side. He even confessed to her that he had massacred an entire Tusken Raider village to avenge his mother, leaving no one alive.
However, when they next met in Star Wars: Episode II – Attack of the Clones, Anakin and Padmé's feelings for one another grew into something resembling love, and their wedding at the end of the film solidified their relationship as one of the most important romances in Star Wars history.
She appeared to have “lost the will to live.” The most common theory states that perhaps Palpatine used Padme's life force to heal the barely alive Anakin. Evidence In support of this theory includes how Padme appeared to die right when Anakin/Darth Vader's life-saving procedure was over.