Cassyon was the youngest of Bretonnia's Dukes, nonetheless he was a mighty Grail Knight who rode atop a fearsome Royal Pegasus. His father died whilst Cassyon was questing for the Grail, and the young Duke knew nothing of his status until he returned to Parravon as a Living Saint.
Cassyon is an open and enthusiastic young man, bearing no malice towards anyone, which makes it almost impossible for people to dislike him. On the other hand he believes he can fulfill his ducal duties simply by riding across the skies, smiting enemies and striking down monsters. There is no doubt that he excels at this, but there are matters of taxation, justice and administration as well, much to his counselors frustration.
Duke Cassyons prowess in combat has not escaped the notice of the Parravonese, and the story that he is Duke Agilgar reborn has recently started to spread.
The young Duke fought against the Empire at Axe Bite Pass, coming to Montforts aid whilst Tristan le Troubadour hunted down a traitor to Bretonnia. True to his beliefs, the young Grail Knight soared away as soon as Bretonnia was victorious, likely searching for more foes to smite... much to Tristan's frustration.