He couldn't bring himself to kill Darth Vader, however, because he continues to associate him with the Anakin he trained as a boy. This is also the exact reason why Obi-Wan didn't kill Anakin on Mustafar despite the opportunity a decade earlier in Star Wars: Episode III - Revenge of the Sith.
Obi-Wan knew it was only a matter of time. So, he made the difficult decision to use his learnings and become one with the force, rather than let Vader decapitate him.
While Obi-Wan Kenobi was frail by the time of Star Wars: A New Hope, he was still stronger with the Force than Darth Vader.
In Star Wars Legends and Canon, Galen Marek (Starkiller) is the only Jedi (other than Obi-Wan Kenobi) to put a beat down on Darth Vader/Anakin Skywalker.
Firstly, he hasn't fought in years. In order to hide from the Empire, he needed to keep a low profile. This means that he's not in his best fighting form. Couple that with his wavering faith and he isn't really attuned with the Force, further impeding his fighting skills.
Anakin admits to Obi-Wan that he has been arrogant and unappreciative of his training, and apologizes to his master. Obi-Wan assures Anakin that he is proud of him, telling him that he has become a "far greater Jedi than I could ever hope to be."
1 Darth Sidious
There has been no Sith, as powerful, meticulous, nor as evil as the Emperor himself, Darth Sidious. As previously mentioned, Sidious trained in the Dark Side by Darth Plagueis before Sidious killed Plagueis in his sleep, making Sidious a Sith Master.
Biography. Legend had it that Yoda—a Jedi who became Grand Master—was trained by N'Kata Del Gormo.
Plo Koon. Wise and compassionate, Plo Koon was one of the most effective Jedi masters, genuinely caring about the clones he commanded.
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.
Vader responded “I am not your failure, Obi-Wan. You didn't kill Anakin Skywalker. I did.” This allows Obi-Wan to finally accept that Anakin is truly gone and that there was nothing he could have realistically done to save him.
Before he discovered Vader had survived Mustafar, Obi-wan lived with the regret of killing his son, brother and best friend. After, he regretted not killing him and wondered if he had only made things worse by pushing Anakin further into dark side and Palpatine's arms.
Yes, when Darth Vader turned back to Anakin Skywalker and sacrifice himself to save his son, he dies and Obi-Wan uses the force to connect with Anakin's spirit. In that time Anakin apologizes to Obi-Wan, desperately asking him to forgive him for everything he has done to him and everybody over the years.
“I'm not your failure, Obi-Wan,” Vader says. “You didn't kill Anakin Skywalker. I did.” This allows Obi-Wan to finally let go of all his guilt over Anakin's transformation into Darth Vader.
In the material around the film from the Legends timeline, it's established that by the end of Star Wars: Episode III - Revenge of the Sith, Kenobi was one of the characters who knew Anakin's Sith name was Darth Vader. However, what he didn't know was that he was still alive after Mustafar.
Obi-Wan knew Anakin through and through and understood his overconfidence and arrogance. He knew Anakin would fight with rage and aggression, while he remained cool and calculated. Pairing his understanding of Anakin with his knowledge of Soresu ultimately gave him the upper hand in the battle.
Visions of Obi-Wan. The comic opens during the last moments of Revenge of the Sith, recreating the well-memed instance when a despondent, freshly-armored Vader cries out with a drawling “nooooooo” over how much he's lost.
Yes, Vader regreted what he had become, but he thought it was to late to turn back until he felt love again.
In contrast, Vader sensed his connection to Luke Skywalker almost immediately. How did Vader detect his relationship with one of his offspring but not the other? The short answer is that creator George Lucas had no idea Leia would end up becoming Darth Vader's daughter.
The Third Sister was at the Jedi Temple during Order 66. She either saw Anakin kill her fellow Jedi or saw the recording of his crimes. That's why she has such hatred for Obi-Wan. She was a Padawan who escaped Order 66.
Vader learned that Leia was his daughter by sensing it from Luke in Return of the Jedi.
Arguably, some of the rarest types of Jedi were the so-called Iron Knights. These are members of the Shards species - crystals with a brain of their own. They were Force-sensitive and all trained under the tutelage of Jedi Master Aqinos. The Shards had droid bodies, similar to that of General Grievous.
Coleman Trebor
He was the Jedi that looked more or less like a bipedal dinosaur with opposable thumbs. Coleman Trebor is by far the weakest Jedi to ever exist. He made his movie appearance in Attack Of The Clones.