|Alias||"Knight King Cassius"|
|Occupation||King of the Northern Kingdom (formerly), Leader of Saint Haven (formerly)|
|Relatives||Cassius III (descendant)|
|Current Location||Saint Haven (possible burial location)|
Cassius I was a former King of the Northern Kingdom and leader of Saint Haven, known for his title "Knight King". During an expedition in the deserts near Tel Numara, he awakened the powerful Desert Dragon Jakard. However, instead of confronting the beast, he began an intimate friendship with the dragon of the desert, which was tested not only by their nature, but their respective circumstances.
Before becoming the king of Saint Haven, Cassius was a knight affiliated to the Northern Kingdom. During a royal expedition to the deserts surrounding Tel Numara, he stumbled upon a girl with yellow hair. The girl introduced herself as Jakard, the Desert Dragon, and she showed a lack of interest in the humans who trespassed her domain. However, Cassius immediately wanted to know more about the yellow-haired stranger, something that confused the dragon. Nonetheless, she accepted the knight's offer and stepped outside of the desert to join his adventures.
For some time, Cassius and Jakard—now known to the humans under the name Aisha—fought together alongside the soldiers of Saint Haven. Their relationship also improved during this time; in one instance, Cassius made a red ribbon as a gift to Aisha after noticing that her hair lacked any accessories. Eventually, however, Aisha decided to part ways with Cassius after he rose to the throne as the next king of Saint Haven.
Both Cassius and Jakard were saddened by their separation. They eventually reunited together, but this meeting was different, as it involved the kingdom expanding their land and encroaching Jakard's domain under the advise of General Tirus and the Minister at that time. Concerned of the dragon's well-being, Cassius traveled to the desert, only to listen to his injured soldiers calling Aisha a monster. He managed to see Aisha as well, but the heartbroken dragon saw Cassius' presence with the soldiers of Saint Haven as a sign of betrayal. As a result, Jakard decided to "test his trustworthiness" by engaging him in combat.
The fight ended with Jakard falling under Cassius' sword, putting an end to an expedition that cost many of Saint Haven's soldiers. However, Cassius himself thought that Jakard hesitated to slay him at the decisive moment, and he blamed himself for not being able to show him the trust that the beast demanded.
Not long after the Desert Dragon Raid, it is said that Cassius peacefully died in his sleep. The sudden death of the king of Saint Haven, especially after losing another king during the history of the kingdom, saddened the subjects he left behind. He also died without fully acknowledging his achievement of slaying the Desert Dragon, causing many people to be unable to recognize his feat. It was only much later that records of a group of adventurers slaying the Black Dragon were accepted by many, causing it to be recorded as the first instance of humans slaying a dragon.