Warning: SPOILERS for Obi-Wan Kenobi episode 3.
Who is Obi-Wan Kenobi's brother, and has he appeared in any of the Star Wars movies, shows, or books? Most Jedi were taken in by the Jedi Order at an early age, presumably shortly after birth, once they had begun showing signs of Force sensitivity. Meanwhile, Anakin Skywalker was deemed too old to begin training, but it was Qui-Gon Jinn's persistence and subsequent death that ultimately led to the boy being trained.
Obi-Wan never had the luxury of choosing what to do with his life, as he joined the Jedi when he was just a child. Interestingly, in Obi-Wan Kenobi episode 3, Obi-Wan mentions remembering glimpses of his parents, which isn't too surprising given Leia Organa also told Luke Skywalker in Return of the Jedi that she remembered her mother, despite only seeing her for a brief moment when she was born. But the most shocking reveal in this scene in Obi-Wan Kenobi is that Obi-Wan confirms he has a brother. So, who is Obi-Wan's brother?
Obi-Wan Kenobi's brother has never been named in Star Wars canon, but the original plan was for him to be Owen Lars. Way back when George Lucas was developing the story for Return of the Jedi, he planned to reveal that Owen Lars was Obi-Wan's brother, but that never made it into the final version of the story; however, various materials that came out afterward maintained the idea of Owen and Obi-Wan being related. It wasn't until Star Wars: Episode II - Attack of the Clones that the plan changed, and Owen Lars was officially confirmed as Anakin Skywalker's step-brother.
Is Owen Lars Actually Obi-Wan Kenobi's Brother?
In current Star Wars canon, no, Owen Lars isn't Obi-Wan Kenobi's brother. Thing is, the reveal in Attack of the Clones complicated what people believed of Kenobi's backstory. During his time as Qui-Gon Jinn's apprentice, Obi-Wan had dreams of his family, including a brother named Owen. But when Obi-Wan learned of Anakin's step-brother during the Clone Wars, he began questioning the legitimacy of his dreams. It wasn't until 2015 that Star Wars finally explained that Obi-Wan's dreams of Owen weren't visions of his brother, but rather visions of the future, as he was actually dreaming about Owen Lars, not Owen Kenobi.
So unfortunately, Star Wars hasn't officially revealed Obi-Wan Kenobi's real brother in canon yet, but since he was brought up in episode 3, perhaps it's something that will happen in the future - either in this series or in another project from Lucasfilm. The thing is, if Owen Lars did end up being Obi-Wan Kenobi's brother, that would've reframed two aspects from the original trilogy; one, Obi-Wan not reacting to Owen's death would've been distasteful, and two, hiding Luke with his brother would've explained why the Inquisitors never found Luke on Tatooine. But George Lucas never went down that path.
New episodes of Obi-Wan Kenobi release on Wednesdays on Disney+.