Eithan Arelius begins as an Underlord in the series. He advances to Archlord and even beyond. One of the main characters, he acts as the mentor of the group having adopted both Yerin Arelius and Wei Shi Lindon Arelius into his family. He also forms close ties with Orthos the sacred dragon-turtle, horned-warrior Ziel of the Wastelands and Akura Mercy.
When Yerin asked him why he wanted to mentor them, he replied: “I have been looking for people to walk with me every step of the way.” “Where to?” she asked. “To the end.” He let that hang in the air, resonating with honest yearning like a pure musical note. The end of the sacred arts. It was the definition of a myth, the unattainable goal sought by every Path.
Eithan has another goal, to rid the world of self-centered monarchs and of dreadgods. Internally, he thinks: 'If Reigan Shen didn’t die to a new generation of Monarchs raised by Eithan, that would be the real tragedy.' (Wintersteel)
Eithan Arelius was one of the advisers of the Tiberian Arelius, the Arelius monarch, before he (the monarch) died. He was born on the Rosegold continent but he lived most of his childhood in the Blackflame empire on the Ashwind continent. He was able to do this because of a portal that opens once every ten years between the two continents. He returned to the Blackflame empire in his mid 20s and became the patriarch of the side branch of the Arelius family. At this time, Eithan was an underlord. This was also after Tiberian's death.
In Cradle Book 10 Reaper, we find out who Eithan actually is. Spoiler:
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Eithan is actually Ozriel the Reaper, a member of the Abidan Court, with his spirit suppressed. When the Mad King descends on Cradle, he is forced to reveal his true form to stop Cradle from being destroyed, and the Abidan takes him away.
Gradually we learn that Eithan's third goal is for his students to ascend beyond Cradle and become reapers, of a sort, to fulfill the original goal of the executor program