Inquisitorius

The Inquisitorius was an organization of Force-sensitive Dark warriors formed after the fall of the Galactic Republic by the Galactic Empire. Trained by Darth Vader, the Inquisitors hunted down and killed any Jedi Knights that survived Order 66, which wiped out most of the Jedi Order. Among their many victims was Luminara Unduli. In addition to killing Jedi, the Inquisitors were tasked with finding any Force-sensitive children scattered throughout the galaxy and either kill them or shanghai them into service. They were led by the Grand Inquisitor. Of the order and including the Grand Inquisitor himself, seven Inquisitors (four in-series and three others (one in the tie-in novel, Ahsoka) and another two shown in the Darth Vader series by Marvel Comics) have been seen thus far, but there may very well be many more, given that their number ranks go as high as eight. Some, like the Grand Inquisitor himself, were once Jedi, giving them an added edge in their hunts to exterminate the latter from the galaxy.

Background
The Inquisitors formed shortly after the fall of the Galactic Republic and began hunting down any Jedi that survived the Jedi Purge. Once Jedi and Force Sensitives that turned to the Dark side, they were made into disciples and servants of the Sith by Palpatine, who gave command of them to Lord Vader after he successfully built his own Sith lightsaber. One of their most notable victims was the Jedi Master Luminara Unduli. Luminara's skeleton was kept by them to lure in other Jedi to their deaths.

Ability-wise, Inquisitors were strong, but relied mostly on brute strength and intimidation to defeat their enemies. However, most of the Inquisitors were no match for Jedi Masters or sufficiently trained Force-sensitives in skill.

By the time of the Battle of Yavin, the Inquisitors became redundant, as virtually no more Jedi were left to hunt by that time. Because of this and likely because of Palpatine's fear of rival Force-users, the Inquisitors eventually ceased to exist, leaving only Palpatine, Anakin Skywalker/Darth Vader, Obi-Wan Kenobi, Yoda, Luke Skywalker and Leia Organa as the only known Force-users by that time.

Organization
The Inquisitors were led by the Grand Inquisitor, and answered only to the Sith, their masters. Darth Vader commanded all Inquisitors, including the Grand Inquisitor.

In terms of rank, Grand Inquisitor was the highest ranking title bestowed on them. All inquisitors beneath that referred to each other by the title of Sister or Brother depending on Gender and by the rank they had attained. Such examples included the Seventh Sister and the Fifth Brother. Despite their mutual goal of hunting Jedi, the Inquisitors competed fiercely against one another to attain higher ranks. When one was killed, the others of lower rank would compete to claim the rank that had opened up. The Inquisitors also hunted for Jedi and Sith artifacts and potential rivals to the Sith's regime as well; for example, the Eighth Brother was dispatched to hunt down Darth Maul and retrieve the Sith Holocron he was after.

Powers and Equipment

 * The Force: The Inquisitors were skilled in the ways of the Force, particularly the Dark side of the Force. They learned from the Sith that commanded them, or from the Jedi Order they once served before unknown circumstances turned them to the Dark side. Though some were highly skilled, they were closely watched by Vader and Palpatine to ensure they never became too powerful.
 * Lightsabers: All Inquisitors were armed with gyroscopic double-bladed red lightsabers that allowed them to win duels quickly and easily by unnerving their opponents using the spinning function. However, these lightsabers had a weakness in that the openings in the hilt made it easy to destroy it by slicing the spinning components apart. They could also be utilized for flight in a similar manner to a helicopter. The Kyber crystals powering these weapons were stolen from the Jedi Temple and likely from the weapons of fallen Jedi, and were turned red through corruption of the Dark side of the Force, which was known as "making the crystal bleed".

Star Wars Rebels
The Grand Inquisitor and his subordinates were dispatched by Darth Vader five years before the Battle of Yavin to hunt down the children of the Force, so that young Force-sensitives could not become Jedi. The Grand Inquisitor would later go after Ezra Bridger and Kanan Jarrus, whom he had been alerted to by Agent Kallus. Kallus' intel allowed the Grand Inquisitor to eventually capture Kanan after a long pursuit, but Ezra and the crew of the Ghost rescued him and Kanan defeated the Inquisitor, who, knowing he had failed, killed himself instead of awaiting the punishment he would face at the hands of Darth Vader.

Darth Vader would then send Fifth Brother and Seventh Sister to hunt Ezra, Kanan and the rest of the Rebels. The two Inquisitors also had a priority of hunting down any Force-sensitive infant they could find, but were thwarted by Kanan, Ezra and Ahsoka Tano, whom they were also hunting. They continued hunting the Jedi, and eventually faced off against them and Darth Maul on Malachor with the Eighth Brother. All three Inquisitors were killed as Vader arrived to finish what they started and claim the Sith temple on Malachor they had found for the Emperor.

Ahsoka
The Inquisitor known as the Sixth Brother hunted for and eventually tracked down Ahsoka Tano during her days on the run from the Empire. However, Ahsoka proved to be more than a match for him, killing him and taking his lightsaber components and imbuing the Kyber crystals with the Light side of the Force to construct her two white-bladed lightsabers.

Comics
The Inquisitorius first appear in the Marvel Comics Star Wars series Darth Vader: Dark Lord of the Sith: The Chosen One Part VI. Darth Vader is sent by Palpatine to investigate an intruder in the Jedi Temple and confronts the Grand Inquisitor in the temple's library. The Sith Lord easily defeats the Dark side acolyte and spares him on Palpatine's orders after revealing that the Grand Inquisitor is a servant of the Empire. Palpatine then takes Vader to his old lair in Coruscant's Industrial Discrict, where he presents the Inquisitorius to Vader and places them under his command to hunt any surviving Jedi. In addition to the Grand Inquisitor, Seventh Sister, Fifth Brother, and Eighth Brother who all appear in this issue, two new inquisitors are show in this comic; one of which is a huge and hulking alien called a Dowutin with tusks sticking out of his chin, and the other being an unknown alien species with gray skin and wearing armor that covers most of his face.

Trivia

 * The Inquisitorius first appeared The Star Wars Sourcebook in 1987 for Star Wars: The Roleplaying Game written by Curtis Smith and Bill Slavicsek.  Their role was later expanded in many other sources of the Star Wars Expanded Universe now known as Legends which is declared non-canon. The Inquisitorius was later re-canonized in Star Wars Rebels which also has many re-canonized Legends material as well.
 * The episode "Always Two There Are" hints that the Inquisitors are somewhat distanced from the rest of the Imperial Army. It also implies that there is fierce competition between Inquisitors.
 * The Inquisitors are a concept that had appeared in numerous Star Wars media (from which the name "Inquisitorius" stems), though Rebels is the first canon material to feature them since Disney bought out Lucasfilm.
 * All of the Inquisitors introduced thus far have been non-humans, which is something of an abnormality in the Empire given its historical prejudices against nonhumans. This is likely due to their Force abilities, as was the case with Maul.
 * The Inquisitors seem to have ceased to exist by the time of A New Hope, as Darth Vader was said by Wilhuff Tarkin to be the only Force-wielder in the Emperor's service, which means the Inquisitors must have been disbanded or all deceased at the time. Pablo Hidalgo has noted that the Inquisitors were most likely few in number.