Early on in your tribe's wandering history, when they first came out of the east from between the world's edge mountains into the old world, they were hired by the then-ruler of Akendorf in the border princes to help secure his realm. First against his rivals, and then against a tide of beasts and monsters that had recently come pouring out of the Düsterwald forest.
At first, the tribe feasted well on the endless hordes of Mutants and Wolf-beasts crushed beneath their steel boots. The tables soon turned, however, when the leader of the beastmen revealed himself.
A great prophet and Shaman of the brayherds, gifted with unholy powers by the dark gods, this fell creature unleashed terrible sorcery upon your tribe's warhost, reducing entire bands of warriors to little more than molten bone-liquid, while the nearby beastmen seemed to only grow in might and ferocity, inspired by it's presence.
The tribe's pride broke when the then-Tyrant was twisted into a deformed, bestial mutant and turned on his own warriors, causing them to flee the field. The Shaman had dealt the tribe one of it's few, and earliest defeats.
Twelve times since then has the Shaman known as Mooneyes met the Ironjaw tribe on the field of battle, claiming the lives of a further three Tyrants. Of all those battles, it was only forced to retreat twice.
Nobody knows why the two encounter each other so often. Perhaps mooneyes has a special vendetta against the tribe, or perhaps the architect of fate simply finds it amusing to put them in eachothers path. Whatever the reason, Mooneyes has become the eternal specter haunting the minds of the Ironjaw tribe.
Thankfully you have never had the displeasure of meeting it in person, but Mooneyes has become something like the collective nightmare of the tribe. The scary story told around campfires to get the young'uns to behave. Every such story ends with a warning:
Do not wander alone at night, do not stray far from the campfire. For out there, in the dark of the night, lurk the balefully glowing eyes of the great terror. Once they see you, it is already too late.