The answer is obvious.
Luke Skywalker finally met his end in The Last Jedi, which was the most polarizing Star Wars film to date. After using all of his strength to project himself across the galaxy to confront Kylo Ren, Luke willingly let his physical form go as he joined the world of the force. Mark Hamill, who has been playing Luke since the late '70s, confirmed that he will be back for The Rise of Skywalker, but he hopes that it will be his last appearance in the franchise.
While attending the Child’s Play premiere, the Associated Press questioned Hamill about his role in The Rise of Skywalker. "I sure hope so," answered Hamill with a laugh when asked if he was finally done with the Star Wars franchise. "I had closure in the last one," he continued. "The fact that I'm involved in any capacity is only because of that peculiar aspect of the Star Wars mythology where if you're a Jedi you get to come back and make a curtain call as a Force ghost." Hamill revealing exactly how he will be involved in The Rise Of Skywalker may cause some executives at Disney to shake their heads, but this isn't a very big revelation. Star Wars has been bringing back "dead" characters since Obi-Wan.