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.
Obi-Wan greets R2-D2 and later recalls “not owning a droid.” Obi-Wan purposely withheld information from Luke in order to keep Luke from straying away. This could offer an explanation as to why he appears to not know who R2-D2 is. Further in Empire Strikes Back, neither Yoda nor Darth Vader recognizes either droid.
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.
His memory was wiped at the end of Revenge of the Sith. A blabbermouth like him can't be trusted with sensitive information.
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.
Revenge of the Sith
After Anakin falls to the dark side of the Force and becomes Darth Vader, he takes R2-D2 with him when he goes to assassinate the Separatist council, but tells him to stay with the ship.
The Clone Wars were fought for three years, with Obi-Wan being 38 by the time the conflict was ending. In other words, Obi-Wan was 38 years old during Revenge of the Sith. As a comparison, Ewan McGregor was 28 during The Phantom Menace and 34 during Revenge of the Sith.
Vader agreed to help the handmaiden, silently recalling the time he spent with Padmé in the process. In this moment, he was once again Anakin Skywalker, a young man in love who simply wanted to change the world for the better.
R2-D2 was in on the scheme to keep the secret away from Luke and Leia. He was devoted to the Skywalker family, and at the guidance of Obi-wan and Yoda, he would have maintained that secret in order to help protect the twins.
Theory 1: Leia Doesn't Remember Ben Is Obi-Wan
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.
Anakin Skywalker is the son of Shmi Skywalker, born without a father through the Force. He is the secret husband of Padmé Amidala, the father of Luke Skywalker and Leia Organa, the father-in-law of Han Solo, and the maternal grandfather of Ben Solo.
Does Darth Vader remember being Anakin? Yes. Yes, he remembers his name but feels it has no meaning to him anymore.
After Cad Bane had kidnapped and ransacked the memory of C-3PO and R2-D2 for information on the Senate Building's layout, he only had the incident wiped from their memories to avoid having any suspicion falling on him.
Threepio had his memory wiped at the end of Revenge of the Sith. He doesn't even know Anakin was Anakin.
Chewbacca - didn't know anything of import re: Anakin or Obi-wan. He fought with Yoda, but didn't know much else about him after helping him flee from Order 66.
Anakin does not have even the slightest bit of remorse. By the end, he feels nothing but anger. Although he feels regret for killing Padme, he still helps the evil Emperor. The film ends with Anakins standing side by side with the man on whose behalf he has committed all his crimes.
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.
During the Imperial Era, a human female nurse served the Galactic Empire on board the Death Star under the supervision of a doctor. They both served the Sith Lord Darth Vader as his personal medical caretakers. The nurse became obsessed and psychotically in love with the Dark Lord of the Sith.
Why does Obi-Wan Kenobi age like that? Because he's not real, and is a fictional character played by different people. You see, Obi-Wan Kenobi is played by Alec Guinness in the original trilogy. Guinness was 62 when he filmed A New Hope, and he died in 2000.
In the story, we learn that Obi-Wan took on the name Ben because it's a nickname given to him by an old flame, the Duchess Satine Kryze. He takes on the name because it still has emotional resonance for him.
In the original Star Wars: Episode VI – Return of the Jedi screenplay, Obi-Wan did have a brother, and it was none other than Owen Lars (Joel Edgerton)—Luke Skywalker's step-uncle and Anakin's step-brother.
According to the comics (which are canon), yes. See this image below: This came from Cloud City (Bespin). Remember that this is the first (and only) time Vader saw C3PO after RoTS.
As such, R2D2 appears to be the state property of Naboo. Queen Amidala as the head of state exercised her control over R2D2. The Droid continued his service to Amidala while she was a Senator.
Star Wars Characters That Can Understand Droids
While all droids understand Binary, only a handful of living creatures can. Canon characters, such as Anakin Skywalker, whose relationship with R2-D2 is one of the best in the whole series, Rey, Poe Dameron, Hera Snydulla and Kazuda Xiono are fluent in the droid language.