Like many Sith masters and their apprentices, Emperor Palpatine and Darth Vader have fought and clashed several times in the established Star Wars canon. Having become Palpatine's apprentice during Revenge of the Sith, there were multiple instances in which Vader attempted to defy and even kill his master. While Palpatine clearly bested his apprentice time and time again up until Vader's redemption in Return of the Jedi, some encounters were closer than others (and some even ended in stalemates).

According to Darth Bane's Rule of Two, there must always be a master to embody the dark side of the Force, and an apprentice to crave it. The apprentice is meant to gain enough power to eventually overthrow and kill the master, becoming a new Sith Lord with their own pupil. As such, it shouldn't be much of a surprise to learn that Vader tried killing Palpatine using the dark side...