Star Wars is filled with plenty of villains using the Dark Side of the Force. The Sith present a terrifying foe for anyone siding with the Republic, the Rebellion, or the Resistance, because they have Force powers and aren't afraid to cross lines with how they use those abilities. These powers can be terrible if left unchecked.
But there are some heroes in Star Wars who already push boundaries while siding with the Light Side Force users. If these people were ever able to control the Dark Side of the Force, they would become some of the most terrifying villains in Star Wars lore.
9 Jar Jar Binks
This one has been a popular theory among Star Wars fans. It's been rumored by the fandom that George Lucas intended to reveal Jar Jar Binks as a Sith Lord before the negative reaction to the character forced him to change his mind. While that's never been confirmed, it raises some interesting questions.
Jar Jar, as a fill-in for Senator Amidala, suggests giving Chancellor Palpatine the emergency powers that lead to him becoming Emperor. Even some of his actions in The Phantom Menace, that are written off as bumbling, could have been the cunning actions of a Sith Lord. Darth Jar Jar is an interesting concept.
8 Rey
It's teased throughout the entire sequel trilogy that Rey could turn to the Dark Side. Her connection to Kylo Ren made it almost impossible for her to escape the Dark Side. Plus, viewers got a fully depicted Dark Rey scene in The Rise of Skywalker.
Rey showed natural Force abilities from the moment she first appears onscreen in The Force Awakens, but she always makes the decision to side with the Light Side. Still, it's hard to argue she could have been devastating if she turned evil. She is a Palpatine after all, and somehow, he returned.
7 Ezra Bridger
Ezra is another Force user that flirted with the Dark Side, but always came back around to the Light Side. Ezra started interacting with the Sith Holocron in season three of Rebels, leading to him becoming more brutal in his fights. He even forced a stormtrooper to turn on his fellow clones before walking off a platform to his death.
Eventually, Ezra saw the error of his ways, and fought alongside his fellow Rebels and thwarted Grand Admiral Thrawn. Still, if Ezra had given in more, either to the Sith Holocron, or even his interactions with Darth Maul, he would have been one of the most evil Sith in the galaxy.
6 Mace Windu
Mace Windu stood next to Yoda as the leaders of the Jedi Council, but Samuel L Jackson's performance made it seem like there was an edge of the Dark Side to his Force abilities. While he always fought with the Light Side, it always seemed like Mace Windu was more anti-hero than hero.
In Attack of the Clones, Mace Windu beheaded Jango Fett in front of his son, Boba. Though Jango needed to be defeated, decapitation wasn't the only solution, and a young boy certainly didn't need to witness his own father's brutal death. In Revenge of the Sith, Windu appears to have Darth Sidious defeated, and is willing to kill him rather than force him to stand trial. If he's willing to kill in these instance, imagine what he would do without restraint.
5 Qui-Gon Jinn
While not as powerful as some other Jedi, Qui-Gon Jinn developed an intriguing relationship with the Force. He believed the Council was losing its way and dedicated his life to the Living Force. This allowed him to access the ability to communicate from beyond the grave, a training he passed on to Yoda and Obi-Wan even after his death.
Imagine someone who was in touch with the Living Force, but willing to use it for the Dark Side. With all the powers Darth Sidious and Darth Vader were able to command, they still never reached the level of Obi-Wan and Yoda, who were able to returns as Force ghosts and not have to rely on cloning. That would be a dangerous power to pass along to the Dark Side users.
4 Ahsoka Tano
Ahsoka is one of the few Jedi to become disillusioned with the Jedi Order who didn't fall to the Dark Side. She became a neutral Force user, wielding white lightsabers and showing that she didn't believe in the teachings of either the Sith or the Jedi.
However, in season three of The Clone Wars, Ahsoka is put under a dark spell, and it demonstrates what she probably would have been like had she joined the Sith. Ahsoka was eager to fight and was fueled by anger. She could have gone on a devastating rampage if she gave in to the Dark Side.
3 Yoda
Yoda is one of the top two Force users seen in all of Star Wars. He beats Count Dooku in battle after Dooku has defeated Obi-Wan Kenobi and Anakin Skywalker at the same time. He stands toe-to-toe with Darth Sidious, and although he fails in his mission, he still walks away and is able to train Luke later in life.
Yoda lived to be 900 years old, and trained hundreds of Jedi in the Light Side of the Force. If he had fallen, he would have had a long and devastating reign as a Sith. He would've been one of the harder Sith Lords to kill, meaning by the rule of two, he would have gone through several apprentices. That is terrifying.
2 Obi-Wan Kenobi
This one is the least likely person to ever turn to the Dark Side, which is why Obi-Wan Kenobi would be one of the more terrifying Sith if he did turn. Obi-Wan is one of the mentally strongest Jedi, which would make him an even more devastating foe if he turned against the Jedi.
Obi-Wan cut Darth Maul in half and defeated General Grievous in enough time to get his lightsaber back before the execution of Order 66. Even though he couldn't kill his now former friend on Mustafar, he arguably left Anakin Skywalker/Darth Vader to a worse fate by letting him be burned by the lava before Palpatine rescued him and turned Vader into a cyborg.
1 Luke Skywalker
The last hope for the Jedi could have meant the end of the Light Side of the Force if he had fallen to the Dark Side. Obi-Wan and Yoda trained Luke Skywalker through the events of the franchise's first two films, but he isn't ready to take on the Sith by the time he faces Darth Vader and learns about his parentage.
While Luke would not be the last Force sensitive person in history, and it's possible Yoda and Obi-Wan would reach out to Leia, Luke was still the realistic last hope for the Light Side of the Force to survive. And, as shown in The Mandalorian season two finale, Luke became a one-man wrecking crew while fighting the remnants of the Empire. If he had chosen the Dark Side, the Rebellion would have been finished.