S is for Darth Sidious

Darth Sidious aka Emperor Palpatine was the one responsible for corrupting Anakin Skywalker and leading him over to the dark side. He was almost killed by the Master Jedi Mace Windu, but Anakin interceded and saved him.

After surviving Windu, Darth Sidious, taking Anakin, Darth Vader, as his apprentice and together they went on to conquer the galaxy in the name of the Empire.