Though most major Star Wars events are depicted in either a movie or a TV show, some major occurrences happen entirely off-screen, including Obi-Wan Kenobi becoming a member of the Jedi Council. In order for there to be a position for him, one of the established members of the Council had to give up their spot, and Kenobi’s came about due to a great tragedy.
Source：https://www.cbr.com/how-obi-wan-got-seat-jedi-council-star-wars/
