Horsebutt the Enemy, or Heshenaad in the native language, led a campaign against the Empire, which was basically the last act of the Enchanter Wars. His tomb and final resting place is in a canyon in the Golden Sea.

According to Trissiny, chapter 2-13:

"Horsebutt the Enemy was a Stalweiss barbarian cavalry leader who pillaged his way across Imperial territory from the Stalrange to the Golden Sea, where he effectively trapped himself. Indirectly he’s responsible for reuniting the fragments of the Empire, giving the factions a common enemy and a reason to rally together again under the restored Emperor. Some historians think he might have been manipulated into his campaign for exactly that reason. He actually survived within the Sea itself for almost ten years, which made him a severe threat, as no one knew where he’d strike. Even he didn’t; his raiders would just come out of the Sea at whatever random point it spat them out, then vanish back into it. He’s the reason the Empire has such a solid military infrastructure around the frontier, even now."

“Hm,” said Toby thoughtfully. “Sounds like he did the Empire quite a few favors, then, however unintentionally.”

Trissiny nodded. “That’s why he’s remembered as the Enemy. At the time he lived, an enemy was exactly what the Empire needed, something to band together against. If not for him… The continent might be a patchwork of kingdoms again, like in the Age of Adventures. No Empire, no Church, likely no Rail or telescroll networks even if humanity still had the chance to develop those enchantments…”