The Eighth Brother is a Terrelian Jango Jumper Inquisitor who appears briefly in Star Wars Rebels, in the second-season finale "Twilight of the Apprentice" (2016), voiced by Robbie Daymond. He is a specialist tracker deployed alongside the Fifth Brother and Seventh Sister on Malachor.
His death is the most undignified in the Inquisitorius: attempting to flee the fight, he uses a lightsaber already damaged in it, and the spinning mechanism fails at altitude. It is the show making the point that the Inquisitors are equipment as much as they are people, and equipment can be issued faulty. Canon.
Catalogue entry. This figure has a verified record here rather than a full write-up — the encyclopedia labels its own depth instead of padding it.