However, there are Star Wars fan theories suggesting Obi-Wan pretended not to know R2 on purpose. He hid himself away on the planet with the sole purpose of protecting Luke, and during that first meeting, he was still trying to shield the boy from harm.
If Obi-Wan had admitted that he knew R2-D2 and that R2-D2 had belonged to Anakin, Luke may have started asking both of them more questions about his father. To prevent Luke from finding out the full truth before he was ready, Obi-Wan decided to tell more half-truths and pretend he had not known R2-D2 for years.
Darth Vader acts like he doesn't even know C-3PO or R2D2. They were with him since he was a child. He did everything he could to forget his past. Also, his plating had been replaced many times, and protocol droids all look very similar.
What's going on: Anthony Daniels, who plays the C-3PO role in all of the nine Skywalker saga films, recently told HuffPost that he wasn't sure why Obi-Wan Kenobi didn't know C-3PO. He said it's possible Obi-Wan knew too many droids.
Meanwhile, R2-D2's cameo in Obi-Wan Kenobi comes a bit later on at the 38:45 mark of the episode. He's briefly shown on the right side of the screen as Bail and Breha Organa talk about Leia. The appearances of R2-D2 and C-3PO in Obi-Wan Kenobi work perfectly within the established Star Wars canon.
secondly, in Legends, R2 was given programming that actually restricted him. from sharing any information with Luke or Leia. about their parents or relation to one another. this was all part of the plan. to conceal this information from the twins.
In The Phantom Menace, set 32 years before A New Hope, R2-D2 is portrayed as belonging to the Naboo defense forces, one of three astromech droids deployed for repair duty onboard Queen Padmé Amidala's (Natalie Portman) starship as it attempts to get past the Trade Federation blockade.
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.
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.
Because he never owned a droid. R2-D2 was owned by Padme and later Anakin, and after that Bail Organa. R4-P17 was assigned to him to assist, not given to him to own. So he really never owned one.
Towards the end of the war, Anakin turned to the dark side and Padme died so her friend, Bail Organa took the droid as well as R2 when he took her daughter, Leia. C-3PO has his memory wiped unlike R2-D2.
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.
But Anakin remained staunchly against this idea for R2-D2, meaning the droid never had to worry about losing the memories of his past. As a result, R2-D2 could learn the value of intelligence, quick thinking and when and where not to speak up.
C-3PO's memories were (against his own wishes) wiped again on Kijimi when the droidsmith Babu Frik bypassed C-3PO's programming restrictions to allow the droid to translate the Sith writings on a Sith dagger. C-3PO's photoreceptors turned red while he translated the forbidden inscriptions.
After the Clone Wars, however, Brooks Propulsion Devices, the company responsible for the development of his boosters, was shut down, and his rocket boosters were eventually damaged and thus could not be repaired. Despite this, however, R2 hardly regretted the loss of his ability to fly.
R2 was later able to restore his companion during the Battle of Geonosis. 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.
After decades of missions with R2-D2, Luke Skywalker was reasonably fluent in droidspeak. The most common way for binary droids to communicate with organics was by writing, conveyed via another computer system. This is how astromech droid copilots would speak with the pilot of a starfighter.
When Luke Skywalker arrived on Dagobah in 3 ABY, the King of the Dragonsnakes swallowed his astromech droid R2-D2, but then spit the droid back out due to its being indigestible.
The question being answered is: “Do R2D2 and C3PO know that Darth Vader is Anakin?” C-3PO? Definitely not. As many other have pointed out, C-3PO had his memory wiped at the end of Episode III, so it is almost certain that he does not know.
Instead, the diminutive droid appears to have kept his own counsel, perhaps wary of interfering too much in Luke's personal journey. C-3PO lost those memories, but he remained with Han and Leia's family after Return of the Jedi, so can reasonably be assumed to have learned the truth by eavesdropping.
