The Inquisitors are agents of the Sith, but not Sith themselves because they exist outside of the Rule of Two. It's possible that the Inquisitors could've become Sith if they existed in the Old Republic when the Sith Order numbered in the thousands.
History. A dark side warrior with a mysterious past, Kylo Ren was neither Jedi nor Sith, but a product of both sides' teachings. Once an apprentice of Luke Skywalker's, he killed his fellow students and drove Skywalker into exile, becoming a First Order warlord and servant of Supreme Leader Snoke.
How are there Inquisitors if there can only be two Sith?
Star Wars Already Broke The Sith Rule Of Two
While the Sith's Rule of Two was not technically broken by the Inquisitors seeing as they are not members of the Sith, it has in fact been broken many times throughout Star Wars canon and legends.
In contrast to their counterparts, the Sith Warriors, Inquisitors specialized in Force abilities as opposed to martial might, and many would devote much time to researching new skills to survive in the cutthroat Sith political environment. Few acolytes succeeded in becoming Inquisitors.
To become a sith, firstly you must be strong in the force. Then you would need either a Sith Lord to take you in as his apprentice or a sith holocron( containing knowledge of the dark side) to learn the ways of the dark side. Then the apprentice would learn how to use a lightsaber and techniques like force lightning.
Why Are the Inquisitors so WEAK but AMAZING at Hunting Jedi
Can Yoda be a Sith?
Star Wars Confirms Yoda Turned to the Dark Side - and Almost Became the Most Powerful Sith Lord. With the aid of Count Dooku, Yoda could have potentially destroyed the universe if he had gone to the dark side in Star Wars.
There is plenty of debate about the immutability of the Jedi's good and the Sith's evil in Star Wars. Some Sith demonstrate decent, honorable, or outright moral behavior compared to their reputation. Others may have done rotten things in their time, yet fans cannot classify them as entirely or inherently evil.
Reva took a lightsaber blade to the middle twice and survived. Writing aside, she has far more determination and will to live than any of the Inquisitors I just mentioned. And she's still weaker than any named Jedi or Sith.
The Inquisitors' power in the Force varies by the individual. While the Grand Inquisitor is the strongest of the group, others, like the Tenth Brother, are considerably weaker. Vader and Sidious deliberately didn't teach the Inquisitors the true ways of the Sith, as their servants may then have truly become threats.
Although it's not fully clear where the Darth moniker originated, Darth Andeddu is thought to be the first character to use the title in-universe. Having originated in Legends, Andeddu was mentioned in the new canon in the comic Star Wars Adventures: Return to Vader's Castle 2, which referenced "Andeddu's flames".
Throughout the conflict, the Rule of Two was violated by Dooku, who took the Dathomirian Nightsister Asajj Ventress on as an assassin and apprentice. However, Sidious, believing Dooku may have been training her to destroy him and sensing that her power had grown, ordered Dooku to eliminate her.
After the Sith were decimated by the Jedi Knights of a thousand years ago, Bane enacted the Sith rule of two: there would be only two active Sith at one time -- a Dark Lord to embody the power, and an apprentice to crave it.
Darth Rey, born Rey Palpatine, was a Force-sensitive Human female who served the Sith Eternal during the New Republic Era. She fought on the side of the First Order in the war against the Resistance.
Count Dooku was a Force-sensitive Human male Jedi Master who fell to the dark side of the Force and became a Dark Lord of the Sith, known as Darth Tyranus.
Consisting often of former Jedi, the Inquisitors were initially weak in the usage of the dark side of the Force and utilized the defensive fighting discipline common to most of the Jedi Order - which emphasized maintaining a strong defense and only moving to attack when there was no other recourse available.
The first grand inquisitor in Spain was the Dominican Tomás de Torquemada; his name became synonymous with the brutality and fanaticism associated with the Inquisition.
As Palpatine's Sith apprentice, Vader was in charge of the Inquisitors, who quickly came to fear his power. While Vader was far more powerful than the Inquisitors, he was not nearly as sadistic as they were, as shown by their hunting methods and what they did with the Jedi they captured.
In official canon, the Sith were an order of dark side Force users who used their abilities for personal gain. Canonically, the Sith who were not former Jedi include: Darth Sidious. Darth Plagueis.
Essentially, the Inquisitors were former Jedi or Padawans who survived Order 66, but were then turned to the dark side by the Sith. Later, the Inquisitors were a major threat on the Disney+ Star Wars series Obi-Wan Kenobi, and another on the current Star Wars: Ahsoka.
There was one Sith in legends, Vectivus, the Sith who did no evil. He was basically just a brutal businessman with dark side powers. I don't know much about him but he was definitely less evil than the rest. Although not 'good' in the typical sense of the word, he didn't kill people (I'm pretty sure).
Darth Vectivus was created by Aaron Allston for the first novel of the Star Wars: Legacy of the Force series, Legacy of the Force: Betrayal. He appeared as a spirit to Nelani Dinn and served as a platform for Lumiya to convince Jacen Solo to become Darth Caedus by showing him that not all Sith were necessarily evil.
Emperor Vitiate was a Sith Lord who successfully gained near immortality by draining the life force of an entire planet, later attempting to drain all life in the galaxy, which would give him true immortality.
