Star Wars: 10 Most Powerful Dark Side Force Users
1. Darth Vader (Pre-Suit)
Anakin Skywalker was created by the midichlorians, and was an embodiment of the Force's will. He was the perfect vessel for the Force, and when he fell to the Dark Side, he temporarily had the potential to become the greatest Sith Lord in all of history.
He engaged and killed many Jedi whilst storming the Temple during Order 66, including the Master Swordsman Cin Drallig.
Even after he had his Force powers severely lessened due to the confinements of his life support suit, Vader still took down many Jedi Masters, Knights and Padawans throughout the Jedi Purge.
Whilst utterly consumed by the Dark Side, as he was before he discovered Luke's existence, Vader was a serious threat to Palpatine, who feared Vader would overthrow him.
It's for this reason that Palpatine ensured Vader was vulnerable to attacks from Sith Lightning. Vader's potential for amassing power was immense, and had he defeated Obi-Wan on Mustafar, he would've become the most powerful Dark Side user (and possibly the most powerful Force user) in the galaxy.