Darth Vader

Darth Vader was Anakin Skywalker disembodied after his fight with Obi-Wan Kenobi on Mustafar. Palpatine assured Vader that every Jedi was an enemy of the state, including Kenobi, and it would be endless civil war unless the Jedi were destroyed. Vader was ordered by the Sith Master that, if he wanted to gain enough power in the dark side to save Amidala, he was to lead the 501st Legion into the Jedi Temple and kill every Jedi inside. Vader did this without question, slaughtering venerable Jedi and younglings alike. Vader even killed some Jedi Masters such as Cin Drallig. Some of the Jedi children even approached him, unaware that he was to be their destroyer. The atrocities committed by Vader and the 501st Legion resulted in smoke rising from the pillars of the Jedi Temple, easily visible from the Senate building. This would be the start of the Great Jedi Purge.

Underworld
Vader and Palpatine is confirmed to be in Star Wars: Underworld, but people will talk about him, but they will never show his face and the same with Palpatine.