The Emperor's purge refers collectively to several related campaigns of repression and persecution in the Galactic Empire which were orchestrated by Emperor Palpatine during the Imperial Period, which removed virtually all opposition to his power.
Shortly after assuming political dominion of the known galaxy, Palpatine began to consolidate his power by launching preemptive strikes against numerous enemies, such as political or military personnel who he had been unable to control during his rise to power. Furthermore, any incumbent officers who supposedly held anti-Imperial sentiments were arrested and executed by Admiral Mulleen. His first purge of the Imperial Navy occurred within just two weeks into the Empire's existence, and a notable victim of this was the senior officer, Jace Dallin, who was executed for his loyalty to the Old Republic; Sagoro Autem was also targeted for the purge, but the bounty hunter who "captured" him was actually his son in disguise and he was able to escape Coruscant safely. Another good example of this is the Great Jedi Purge, wherein members of the Jedi Order were denounced as traitors to be executed by Darth Vader and his 501st Legion.