The Fifth Brother is an Inquisitor introduced in the second season of Star Wars Rebels, in "Relics of the Old Republic" (2015), voiced by Philip Anthony-Rodriguez and later played in live action by Sung Kang in Obi-Wan Kenobi (2022). The reference material describes him as humanoid but does not name a species, and that field is left blank here.
He works most often alongside the Seventh Sister, and the pairing is the show's most efficient shorthand for how the Inquisitorius operates: she finds them, he breaks them. He lost his right hand in training with Darth Vader and his left forearm to a Jedi, and died on Malachor at Maul's hand in 3 BBY. 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.