The Grand Inquisitor, commonly known simply as the Inquisitor, was the name adopted by a Pau'an male Jedi Knight who turned to the dark side of the Force and became the leader of the Inquisitorius, a band of Jedi hunters who served the Galactic Empire. The Grand Inquisitor was once a Jedi Temple Guard and was involved in the events surrounding the bombing of the Jedi Temple during the Clone Wars, arresting the innocent and later exonerated Padawan Ahsoka Tano as well as the true culprit, Barriss Offee. After his fall to the dark side, the Grand Inquisitor was responsible for hunting down and eliminating Jedi during the Great Jedi Purge. He personally served the Sith Lord Darth Vader, from whom he received his orders, and was intimately familiar with the records of the Jedi Temple.

The Grand Inquisitor took an active interest in eliminating the rebel crew of the starship Ghost, particularly the Jedi Kanan Jarrus and his Padawan, Ezra Bridger. He encountered these two Jedi on a number of occasions, including a Duel on Stygeon Prime and a duel on the asteroid base Fort Anaxes. After the Grand Inquisitor and the government of Lothal, from which the rebels operated, were consistently unable to eliminate the rebels, Grand Moff Wilhuff Tarkin arrived on Lothal to hunt for the rebels. Together, they captured Jarrus and hoped to use him to learn more about a larger rebel movement that was operating in the galaxy. They brought Jarrus to Mustafar, where the rebels mounted a rescue mission in orbit. During the operation, the Grand Inquisitor engaged Jarrus and Bridger in lightsaber combat, and Jarrus eventually bested him. Rather than face the infamous wrath of Darth Vader for his repeated failures, the Grand Inquisitor chose to fall to his death.

Sometime after his death, a vision of the Grand Inquisitor as his former Jedi Temple Guard self appeared to Jarrus in the Jedi Temple on Lothal. In the vision, this Sentinel warned Jarrus that Bridger could fall to the dark side, and the two engaged in a lightsaber duel. After Jarrus refused to fight any further, the Sentinel knighted Jarrus and told him he was a Jedi Knight as the Grand Inquisitor once was.

The Grand Inquisitor should sound like his voice actor, Jason Issacs.

Example: https://www.youtube.com/watch?v=p10QNI4frfE