Warning: Contains SPOILERS for Star Wars: Darth Vader #46! Emperor Palpatines ultimate defeat in Return of the Jedi is one of the most epic moments in Star Wars history, as it was the climactic moment of the original trilogy that not only featured the defeat of the series villain, but the redemption of Darth Vader himself. The reason Palpatine died is that he underestimated Darth Vader, though interestingly enough, that wasnt the first time Vader defeated Palpatine due to the Emperor underestimating him, with an earlier conflict effectively foreshadowing Palpatines Return of the Jedi death.
https://screenrant.com/palpatine-foreshadows-star-wars-death-underestimating-darth-vader/