My idea for a Jedi Master who survived Order 66, only to be captured and turned into an Inquisitor.
Lenn Shiroh was a skilled pantoran Jedi master who had taken a vow of silence at an early age. A powerful swordsman, he fought skillfully and bravely during the Clone Wars.
His skills enabled him to survive the initial stages of Order 66, but he was ultimately hunted and captured by Darth Vader himself. Under brutal torture, he succumbed to the dark side and joined the Inquisitors.
Vader was aware of Shiroh's vow of silence, and proceeded to sadistically mock it by severing his jaw using his lightsaber during training, flash frying his vocal cords and permanently cutting off his ability to speak. The injury was so damaging and traumatic that he now requires a cybernetic mask to help him breath, like Darth Malak before him.
The Thirteenth Brother, as he is now known, silently and skillfully carries out the Emperor's terrible will across the galaxy.