Abstract
The First Emperor is an almost mythical figure that is worshipped as a god. The true identity of him has since been long forgotten, with each faction that vies over the Empire claiming their faction to be descended from the First Emperor.
The real story of the emperor is unknown, even his name is contested. It is unknown if he had children or any descendants.
Variations
This section will summarize the variations of the Emperor's story that each faction considers true, and then will summarize the real story.
Latins
The Latins believe the First Emperor was a man named Adis, of the Gens Junii. A patrician from a small Latin kingdom that lead armies as a general and fell into good graces with his king.
After that king died, there was a battle for the throne, which ended with Adis himself ascending to the throne.
Adis then embarked on a grand campaign of unification of the Latin kingdoms, with him being proclaimed as "Imperator" (Victorious general). Then he led a vast conquest of all the kingdoms of the continent. The "Conquest" included several military campaigns and diplomatic dealings in order to force the many independent entities to accept the Empire's rule.
At the end, he was hailed as the First Emperor of the unified continent. Seeking to then centralize power, he built a new capital for the Empire, Latium, from where he ruled.
After a long life of conquest, rule and governing. Adis died of old age. His body however, disappeared. Having been taken by the gods and Adis deified, taking his place in Arcadia as a god.
Adis' descendants then ruled for several generations until his family line died out. When this happened, the politicans, senators and generals of the empire faced an issue: Who would replace the Emperor. They couldn't simply elect or pick someone as Emperor, the other factions (which had by then established themselves) would never accept it.
So, to compromise, Imperial Senate enacted the Succession Events as a measure to retain the empire's cohesion. Every 10 years, they'd hold Succession Events, where any faction attend and compete. The winning faction's champion, would then become Emperor.
Pirates
The Pirates believe the First Emperor, to not be an emperor at all, but rather a great captain and admiral, a commander of the greatest pirate fleet to ever sail the seas.
Born Gustav Sommerson to a poor peasant family, living in a coastal town. From here, there are more variations of his story. Some retellings state that he was kidnapped by bandits and sold to slavery before escaping, some say that the village was destroyed by war, some say that he was sold off by his own parents in a desperate attempt to keep the household afloat. And finally, some retellings state he simply left out of a desire for profit.
Regardless, Gustav would end up serving on a Pirate ship. The Ship, named "The Black Lady", named after the ship's Figurehead, which was a statue of Deus Mare, the goddess of the sea, which the crew doused with Black.
Quickly, he rose through the ranks of the ship's crew, eventually becoming its captain. Gustav then engaged a fleet of a trade league. Normally, it's ship were among the strongest, but Gustav attacked as the league's fleet was fleeing from a battle it'd lost. As such, Gustav devastated the fleet. But, more importantly, he extended an invitation to the ship of any of the crews: Overthrow your captain, and we'll welcome you as our own.
Many crews chose to simply side with the Pirates whose promise of gold won them over after a demoralizing loss. As a result, Gustav quickly gained several strong, albeit damaged ships. He immediately set to repairing the ships out of his pocket.
With some of the strongest ships available to him, Gustav devastated the seas with his fleet. His power growing to the point where he became labelled "Sea King", as no ship could set sail without paying him off for safe passage, and those that failed to do so, were set upon, looted and destroyed.
His men grew rich, but Gustav dreamed bigger, he dreamed of a title on the main land, over kings and nations. He began rebuking liscense to sail and set on starving entire kingdoms into submission. When these kingdoms submitted, they were forced not to pay huge sums of money to Gustav, but into submission to The "Sea King".
When nations caught wind of his strategy, it was too late, there were too few kingdoms left to resist and the combined armies of the pirate king, trampled the remaining realms into submission.
Fearing rebellion and instability, Gustav turned to a group of city states he had easily conquered, the Latins. The Latins organized Gustav's empire and gave it laws, structure and most importantly: stability.
From here on, Gustav's story is simiar to Adis', he dies, his descendants rule for a couple generations before the family line dies out, and the largely latin political class, decide to opt for the Succession Events to ensure stability.
The Real Story
Although humanity calls Adis, or Gustav, Imperator Divius, a god born from mortal flesh. The reality is that the Empire was the creation of the gods. Adis, Gustav, whatever you wish to call him, is, in reality the God of systems, structure and organization.
The Empire was created after the fall of Econia, right as Terra was created. The myths were carved into the minds of the various Divines-turned-mortals to create strife between them. The empire, is what the Dungeons were meant to be, a perfect battleground for the lower classes, be they Divines or mortals.
Adis succeeded where Carceres failed.