What defines a true 'Apex predator'?
Is it simply the strongest beast? The most effective hunter? The smartest, most cunning creature? Well, none of these things. It simply must exist at the tip of a food chain, with no predators. It's population is kept down by factors such as competition for resources, high energy consumption, changing environments. There's a lot of examples of these, across the land, skies and seas.
But most of them fall short of the reputation of the Vorax.
The Vorax is a towering furred beast around forty feet long from the base of it's neck to the base of it's tail. It's head and tail resemble that of an alligator in shape, but furred and disproportionately large compared to it's torso. It's torso itself is best compared to a gorilla - incredibly muscular, deceptively squat and almost bipedal in it's resting posture. The first major departure from ordinary biology - aside from it's ridiculous dimensions of course - is the number of limbs the creature has. If one were to somehow view a Vorax resting, and at peace, they would see it has 6 legs, with a second set of shoulders lower and further back from the front pair. Each limb ends in an uncertain number of clawed toes, splayed around a wide downwards-facing palm, with no apparant differentiation between hands and feet.
I skipped over something there, for the sake of beginning somewhere. An 'uncertain number' of clawed toes. You may have noticed the care with which I described the number of limbs it has when at rest. There is good reason for that. Until this point the creature would seem to be an unhealthily large, and strange looking, beast, but unremarkable otherwise. But this is the limit of what can be explained biologically, because the primary reason for this being considered the most dangerous creature without intelligence is that it is not a natural creature in the way most consider the concept.
Of course, given what most people call magic, the supernatural, or anything else 'other' is just as natural as skin and bones, but that is little comfort to a person when a great beast descends upon them, sprounting limbs, wings, further necks and mouths and faces. The beast seemingly knows only desire - it hordes, feasts, and craves. It doesn't display the intelligence enough to do anything with anything it claims, but it shows a clear understanding of ownership, albeit that it believes it owns everything it is aware of. Whenever it finds something it can own, it grows in excitement and continues to change it's form, all the better to claim whatever it seeks.
Of course, this includes the very land around it. The trees, the grass, the rocks. Even alone in the wilderness, it still believes everything is it's own, and will aggressively fight off anything around it. It lacks the actual need to eat for energy - each Vorax seemingly is tied to a series of nodes of energy that tie to certain Primordial forces, but let's ignore that for now - but it will destroy or jealously horde everything it can percieve.
This is also the main reason it doesn't destroy the world around it at large, ironically enough - it possesses many innate unnatural powers, the extend of which is entirely unknown at this time, but it's sensory organs are it's only way of percieving the world, and they are only as good as most predatory beasts. It cannot see to the ends of the earth, and what exists beyond it's perception isn't important when it must expend all it's effort claiming it's own territory. Precisely what it is aware of at any time shifts slightly as it's memory and senses struggle to accomplish it's ever present goal of ownership, and so each Vorax slowly travels across the world, occaisionally clashing with other creatures.
It's just as well they're so rare. I'd like to claim responsibility for that, but I've only seen two myself. The destruction of several of their number, and the seperation of the remainder across the world, lessens the chances that two might breed, presumably. Whether or not they could in the first place is unknown, but I wont berate long dead warriors and magicians for what they didn't know, considering the incredible effort they put into preventing the possibility.