Before various comics, TV shows and movies started to expand on the years between the original Star Wars trilogy and the prequels, very little was known about the period. Canon sources did not provide much insight, and in the time between Order 66 and Luke Skywalker discovering his destiny, there didn't seem to be any Jedi left to stand up against the Empire. However, newer additions to the canon confirm this wasn't the case. Instead, the Empire had a way of silencing rogue Jedi.
The main weapon that the Empire would use in such cases was the Imperial Inquisition, an order of Force-sensitive Jedi hunters cultivated by Palpatine and trained by Vader. While not technically Sith themselves, the Inquisitors could still manipulate the Force and wield deadly weapons. There were more than a few Inquisitors appearing in a variety of media, so let's breakdown the members of this mysterious order.
EDITOR'S NOTE: Updated March 10, 2022, to include Reva, the Third Sister, the Inquisitor officially introduced in the teaser trailer for Obi-Wan Kenobi.
GRAND INQUISITOR
As the leader of the Imperial Inquisition, the Grand Inquisitor was not only the first member of his order introduced in Star Wars: Rebels but also one of the most formidable threats the Ghost crew ever faced. After discovering that Jedi Kanan Jarrus survived Order 66 and was training Ezra Bridger as his Padawan, the Grand Inquisitor took a great personal interest in hunting them down.
After Kanan defeated him in combat, the Grand Inquisitor chose death over facing his master Darth Vader with failure. Although fans never learned the Grand Inquisitor's name, they did gain insight into his history as a Jedi temple guard that was present during Barriss Offee's bombing of the Jedi Temple in The Clone Wars.
SECOND SISTER
As a Jedi Padawan, Trilla Suduri narrowly escaped execution with her master when Order 66 inflicted the Great Jedi Purge on the galaxy. Unfortunately, Suduri was captured by the Empire and subjected to excruciating torture that turned her into a dogged Dark Side loyalist.
Known for her keen intellect and analytical mind, Suduri's capable use of mental and physical force combined with her seeming loyalty made her an ideal candidate for the Inquisitorius. It was not until shortly before her death, when she finally saw the light and made amends with her former master, that she turned away from the Dark Side. For that crime, Darth Vader executed her personally.
THIRD SISTER
After a brief mention in a Star Wars Encyclopedia, fans will finally meet the mysterious Third Sister, Reva in the upcoming Obi-Wan Kenobi. Portrayed by Moses Ingram, the Third Sister served as a member of the Inquisitorius on the trail of the Jedi Master Obi-Wan as the hermit hides out on Tatooine.
Reva's hunt brings her face-to-face with moisture farmer Owen Lars, best known for taking care of Luke Skywalker during his upbringing. Obi-Wan watches over Luke from a distance, but a conflict with the Third Sister could be exactly the kind of threat to bring him out of hiding. The Third Sister is considered ruthlessly ambitious, and alongside her superiors the Grand Inquisitor and Darth Vader himself she certainly needs to be.
FIFTH BROTHER
Unliked the Grand Inquisitor or Trilla Suduri, little is known of Fifth Brother's past before induction into the Imperial Inquisition. All that's clear is that he was among the first recruits who Darth Vader began training when Palpatine tasked his apprentice with honing his Force-sensitive weapons. Vader was a cruel teacher, however, and Fifth Brother lost his right hand in the course of learning his lessons.
Often clashing with his fellow members, Fifth Brother's approach to hunting Jedi was often more brash and direct. When he was on the trail of Ezra Bridger, Seventh Sister once stopped his blade from striking, accusing him of short-sightedness as she explained how Ezra would be useful to them as bait. Fifth Brother clashed with other Dark Side users later, fighting Darth Maul on Malachor before the Sith Lord ended his life.
SIXTH BROTHER
While Fifth Brother may have lost a hand to Vader's training, Sixth Brother lost an entire arm to the Sith lord. The dismemberments came as Vader's way of teaching the Inquisitors to shed their Jedi teaching of fighting defensively, and it was a lesson Sixth Brother took to heart. He fought fiercely, but not quite as fierce as Ahsoka Tano when he tried to hunt her down.
The former Padawan of Vader grew battle-hardened over the years, and during her fight with Sixth Brother, she sensed the kyber crystals calling out to her. She summoned the crystals to her hands, exploding Sixth Brother's weapon and killing him in the process. Ahsoka then used the crystals to forge the white lightsabers she wields in Rebels, now purified of their former owner's tainted Force.
SEVENTH SISTER
None of the other Inquisitors quite seemed to enjoy what they did so much as Seventh Sister, who took great delight when hunting down Jedi. She was one of the main trio responsible for hunting down the Ghost crew following the Grand Inquisitor's death, and her own ambition caused her to see the event as a potential opportunity. Despite her ambition, her journey leads to the same fate as the Fifth Brother, being killed at Maul's hand on Malachor.
EIGHTH BROTHER
Eighth Brother was the third member of the trio to die on Malachor but was unique among the Inquisitorial for his seeming dedication to Palpatine above all. When Darth Vader first claimed leadership of the order, Eighth Brother protested that Palpatine was his only master and it was only the Grand Inquisitor's insistence that put him back in line. Eighth Brother's lightsaber had a unique buzzsaw feature that sprouted blades from its hilt, reflective of his aggressive style, but in the end, it did him little good on Malachor.
NINTH SISTER
While many of the other Inquisitors lost limbs in their training, Ninth Sister actually lost her eye to her new master Vader. As a Jedi, Masana Tide specialized in using the Force to connect with the emotions of others, but the torture and trauma that brought her to the Dark Side robbed her of that bliss. Instead, her talents became twisted toward the arts of interrogation and forcing information out of others. She was perhaps the clearest example of the twisted influence the Dark Side had on former Jedi.
TENTH BROTHER
Prosset Dibs is easily the Inquisitor with the most detailed backstory of his time as Jedi, and the story behind his disillusionment with the Order is one rich with detail. Conflicted by the Jedi's former dedication toward pacifism and their new role as military leaders in the Clone Wars, discontent and turmoil brewed in Prosset's heart. Eventually, he tried to kill Jedi Master Mace Windu and was put onto trial, but Windu spared him of death in lieu of rehabilitation that never took hold.
Prosset's rebellious past made him a perfect candidate for Palpatine's recruitment, and he proved a capable Inquisitor, unhampered by his blindness and in fact more greatly in tune with the senses the Force allowed him. Prosset was further unique in dual-wielding lightsabers during his time as an Inquisitor, seldom employing the dual-bladed spinning options of his fellows. Even his death proved unique, as a Jedi he was hunting instigated Order 66 against Prosset, who as a former member of the Order fell victim to the Stormtrooper's sudden bloodlust.