Calogrenant first appears in Chrétien de Troyes's Yvain, or The Knight with the Lion, written in the 1170s. In Chrétien's tale, Calogrenant is a Knight of the Round Table and the cousin of Yvain, the son of King Urien. He is a man of good birth and fair reputation, though not among the most celebrated knights of the fellowship. His importance lies not in his prowess but in his curiosity, the quality that leads him to ride alone into the forest of Broceliande when other knights are content to remain at court.

The adventure begins at Arthur's Pentecost feast, where the custom holds that the king will not eat until some marvel has been told. The knights sit in silence until Calogrenant rises and asks leave to tell of an adventure that befell him seven years before. He describes how he rode into Broceliande, a place of deep magic where noon is darker than dawn. He met a herdsman, a giant of a man, ugly and misshapen, who tended bulls as large as oxen and who directed him toward a clearing where a marvel awaited. In the clearing Calogrenant found a chapel, and beside it a beautiful tree and an emerald pillar with a silver basin hanging from a chain. A knight would pour water from the basin onto the stone beside the pillar, and immediately a storm would arise, so violent that the heavens seemed to fall.

Calogrenant, unable to resist, poured the water. The storm came instantly, black clouds and hail and wind that stripped the forest bare. From the chapel emerged the Black Knight, guardian of the fountain, furious that his stone had been disturbed. The two knights charged together with such force that both lances shattered, but the Black Knight was the stronger man. He unhorsed Calogrenant, seized his horse by the bridle, and drove him from the clearing in shame, sparing his life but taking his mount and his dignity. Calogrenant returned to court and told no one of his defeat, nursing the wound to his pride in silence for seven years.

At the Pentecost feast, Calogrenant's tale has an effect he never intended. His cousin Yvain, sitting among the knights, is so inflamed by the story that he cannot wait for Arthur's permission to seek the fountain himself. He slips from the hall, mounts his horse, and rides for Broceliande before the king can stop him. Yvain defeats the Black Knight, falls in love with his widow Laudine, and embarks on the adventures that make him the Knight with the Lion, one of the greatest heroes in Arthurian legend. Calogrenant's story, told in modesty and defeat, becomes the seed from which his cousin's glory grows. It is one of the most perfect examples in medieval literature of the tale within the tale, the narrative that exists only to launch a greater narrative.

Calogrenant appears again in later Arthurian tradition, though never with the prominence of his first appearance. In the First Continuation of Chrétien's Perceval, composed around 1200, he is one of the knights killed by the Green Knight, the terrifying challenger whose beheading game would later be made famous by Sir Gawain. In Thomas Malory's Le Morte d'Arthur, compiled around 1470, he appears as Colgrevance, a knight of lesser note who fights in various tournaments and battles but never again tells a story that changes the world. In the German tradition, Hartmann von Aue's Iwein, composed around 1203, gives him the name Kalogrenanz and preserves the fountain episode with the same essential shape: the cousin who fails, the cousin who succeeds, and the story that makes the difference.