Mumbo Jumbo

The Mob’s enforcer, bull-headed, and able to bulk into a heavier form for a fight. He doubles as their driver and gets sent on the occasional undercover job despite being written as slow.

He is the only humanoid character in the series who cannot speak intelligibly, and everyone understands him anyway. That sits oddly against a named voice actor being attributed to him, which is a tension nobody has resolved.

Wikipedia calls him a robotic Minotaur. The ThunderCats wiki refuses to classify him at all, saying it is unclear whether he is robot, alien or android, so we have left the species blank. His pilot appearance is visual materials only, which puts his first real scene in Journey to Limbo. His bird, Airshock, appears in exactly one episode despite being his packaged toy accessory.

Voice. Wikipedia and the ThunderCats wiki both credit Peter Newman, which is consensus rather than a document, and awkward given that the character has no intelligible dialogue.