The Grand Inquisitor was the highest ranking member of the Inquisitorious and the one most feared by Jedi Survivors of Order 66 in hiding across the Galaxy. His very presence carried a cold chill with it and his name sent chills down the spines of those Jedi. But he wasn’t the worst thing they had to worry about. That would be Darth Vader. So how did the Grand Inquisitor slaughter so many Jedi across the Galaxy, despite being nowhere as powerful as Vader?
In the dark days immediately following Order 66, Darth Vader himself was sent to wipe out any Jedi who survived the initial betrayal of the Clone Troopers. Vader was of course very successful in this mission, but eventually Palpatine pulled him away from this duty to help in other important aspects of ruling the new Empire. As a result, Vader was gifted an Order of Force sensitive warriors, who had the sole task of hunting down and killing Jedi survivors wherever they lurked. This was the Order of the Inquisitorious.
Palpatine had been planning for this long before the end of the Clone Wars, and was actually able to turn the Grand Inquisitor the Dark Side before they ended. Palpatine swayed him after the Trial of Barriss Offe, where she tried to frame Ahsoka Tano for attacking the Jedi temple. The Grand Inquisitor is actually the temple guard seen on the left here in this image, and after hearing Barriss’ speec about how the Jedi had lost their way, he agreed and became angered. He was so disilusioned with the Order’s participation in the war, but also by how they treated Ahsoka Tano after she was accused of being behind the attack. Ultimately, this led Palpatine to swoop in and lead him to the darkness…
Now that the Grand Inquisitor was turned, he was ready for the day of ORder 66. On that day, he entered the Temple in his usual Temple guard uniform, and when Anakin marched in with the 501st, he actually helped the new Sith Lord. The Grand Inquisitor ignited his yellow blade and turned on his own temple guard brothers, helping Anakin to wipe every Jedi the temple out. This is actually why you don’t see any Temple Guards in Revenge of the Sith when Anakin arrives, the Grand Inquisitor had already slaughtered them, awaiting Vader’s arrival. On that day alone, the Grand Inquisitor honestly may have racked up a killcount of over 100. Chilling stuff.
Now another reason that the Grand Inquisitor was able to kill so many Jedi in the early days of the Empire was because of the huge resources that Palpatine and Vader put into the inquisitor program. They had informants all across the Galaxy outposts almost everywhere. On top of this, the Grand Inquisitor had a similar sort of status to Vader within the imperial military. When he entered the room, he often outranked even the most respected Moffs and Commanders, simply because he was a force user who answered directly to Vader. Because of this, he could simply pull garrisons of stormtroopers away from other Imperials to use in hunting Jedi, as well as shifting around resources how he saw fit. **If the Grand Inquisitor wanted to lock down and entire city and Execute Order 37 in Order to find a Jedi hiding out there, he had the authority to do so, as he was acting on behalf of Darth Vader.
On top of all of this, at the time he ascended to the position of Grand Inquisitor, most of the Jedi who survived didn’t do so through their skill or force power. Most of them survived through pure luck. Now because the Grand Inquisitor was a member of the Jedi Order for so many years, he had a deep understanding of how much Jedi thought and were trained. Obviously because he witnessed it all for his own eyes.
With this knowledge, the Grand Inquisitor returned the Jedi temple shortly after Order 66 with one singular goal. To learn as much about Lightsaber styles, forms and techniques as possible. He knew that he would be facing many Jedi survivors, so what better way to defeat them, than to learn how they fought precisely. Once he arrived at the temple, a sense of hatred washed over him, because during his time as a Jedi, the Librarian Jocasta Nu never let him access the archives, deeming him unworthy. Now that he was finally able to view the hidden content, the Grand Inquisitor poured tirelessly over every scroll, datapad and file he could find about Lightsaber combat, learning all of its intricacies.