Ambull
A large ape-shaped subterranean desert-dwelling beast that excavates tunnels with iron-hard claws and devours other cave-dwelling creatures with its expandable jaws. The Ambull is originally native to the death world of Luther McIntyre, but nowadays can be found across the Imperium thanks to well-meaning Magos Biologis of the Adeptus Mechanicus spreading the creatures around in attempts at domestication (apparently they taste delicious when properly cooked). Unfortunately the Ambulls have almost always proved to be uncontrollable, tunneling the fuck around, mincing anything that they disliked, and generally becoming an exceedingly dangerous pest on any world they end up infesting. Why nobody thought to simply lobotomize them like Grox is anyone's guess.
On Necromunda, they apparently like to make robotic versions of the Ambull called Ambots. The ambull's brain is placed inside a mechanical body, intended for mining purposes. Of course, the more creative thinking Hive Gangers found a new use for the hulking, chain saw handed ambot; namely as a nigh unstoppable killing machine.
From the description of the Ambull's physical appearance, and their knack for tunneling, there's a certain resemblance to the Umber Hulk, a Dungeons & Dragons monster that predates the creation of 40k.
The Ambull mainly appears on desert worlds but was also encountered on an ice world by the Valhallan 597th and Ciaphas Cain where they were summarily killed and roasted in typical valhalla style
Tabletop
In 2019 the Ambull will finally be coming to the tabletop, in both regular and robotic varieties, via expansions to Blackstone Fortress and Necromunda respectively.
