Ban first appears in Chretien de Troyes's Lancelot, or The Knight of the Cart, written in the 1170s, where he is called the king of Gomeret and mentioned only in passing as the father of the hero. The full story of his life and death was developed in the great thirteenth-century Vulgate Cycle, particularly the Prose Lancelot and the Vulgate Merlin, and was later condensed by Thomas Malory in Le Morte d'Arthur around 1470. In these texts, Ban is the king of Benoic, a realm on the border between Armorican Brittany and Gaul, a land of rivers and marshes where his castle of Trebes stood on an island, reputedly impregnable to any siege.

Ban's closest bond was with his brother Bors, king of Gannes, and the two brothers had married sisters: Ban took Elaine, while Bors took her sister Evaine. Together they ruled the most powerful alliance in Gaul, and their support was essential to any king who wished to claim dominion over the continent. When the young Arthur rose against the rebel kings of Britain, it was Ban and Bors who answered his call, bringing thousands of French knights across the sea to fight at Bedegraine. Their charge broke the rebel line and secured Arthur's throne, and Arthur swore that he would one day repay the debt by aiding them against their own enemies.

That enemy was Claudas, king of the Land Laid Waste, a neighbouring lord who had long coveted the rich lands of Benoic and Gannes. Claudas was patient and cunning, and he knew that no army could take Trebes by storm. Instead he used treachery, sending agents into the castle who set it ablaze from within. The fire spread through the wooden halls, and the defenders, choking on smoke, could not hold the walls. Ban gathered his queen and his infant son and fled through a postern gate, leaving his kingdom to burn behind him.

The flight was desperate. Ban rode through the night with Elaine and the baby, seeking refuge on the road to Arthur's Britain, hoping that the Pendragon would remember his oath and come to their aid. But Arthur was far away, occupied with his own wars, and no help came. Ban reined his horse on a hilltop and looked back at the only home he had ever known. The castle of Trebes was a pillar of fire against the dark, the towers collapsing into the marsh, the banners of Benoic consumed in the blaze. His heart could not bear the sight. He fell from his saddle, clutching his chest, and died on the road, his eyes still fixed on the flames.

Elaine leaped from her horse and ran to her husband, cradling his body and weeping. In her grief she left the infant Lancelot unattended by the roadside, and in that moment the Lady of the Lake, the enchantress Viviane, appeared from the mist and took the child. She would raise him in her underwater palace, teach him to fight and to speak with angels, and one day send him to Arthur's court as the greatest knight the world had ever known. Elaine, bereft of both husband and son, retired to a nunnery and spent her remaining years in prayer. Lancelot would not learn his true parentage until he was a man grown, and when he did, he swore vengeance on Claudas. With his cousins Bors and Lionel he invaded the Land Laid Waste, defeated Claudas, and reclaimed his father's kingdom. But Ban never lived to see it. He remained the king who died looking backward, the father whose legacy was a son he never knew.