Celyddon was an ancient incarnation of Nathaniel, and the brother of Talaith. He was the eldest son of the clan and after his father died he assumed responsibility for his widowed mother and siblings.

In an eerie precursor to his life as Nathaniel, far too much pressure was forced upon Celyddon's young shoulders, and a wedge was driven between him and his one true love, Cassia by her father, Cassius. The Gemellus patriarch admired Celyddon but declared the match impossible because of their class distinctions.

Celyddon was the best friend of Fáelán despite the fact that Fáelán was often an enigma to him. He formed an instant bond with Vericus in childhood, and was distraught when his dear friend and Talaith's beloved, disappeared for four years.

Later on, Celyddon developed a friendship with Vericus' other sister, Illythia, and they began to open up to one another.

Celyddon had an extraordinary spiritual gift and a naturally scientific mind, which Lamagir revered. He remained an ardent follower of Jesus Christ, however, and everything he did was in Jesus' name.

He was the strongest of all in weathering Lamagir's relentless attacks. He was not at Tammabukku as often as others, but swiftly grasped all that was going on around him, and eventually spurned Lamagir.

Celyddon was affected on the deepest level by the evolution of Vericus and Fáelán's relationship. They were his two closest friends and he was stricken with fear that now that they were inseparable, he would be left behind.