In The Secret of Kells, the boy who helps complete the Book of Kells is Brendan.
Brendan is a 12-year-old boy living at the Abbey of Kells under the strict authority of his uncle, Abbot Cellach. His life changes when Brother Aidan arrives from the island monastery of Iona carrying an unfinished illuminated manuscript. Recognizing Brendan's artistic ability, Aidan teaches him how to prepare ink and draw intricate designs.
The story gives Brendan a fictional role in the creation of the historic Book of Kells. To finish the manuscript's final design, he needs the Eye of Colmcille, a crystal lens connected to Saint Colmcille and guarded by the serpent-like spirit Crom Cruach. Brendan's courage and cooperation with the forest spirit Aisling allow him to recover it.
Years later, Brendan and Aidan continue their work in exile. When Brendan returns to Kells as an adult, he uses a page preserved by Cellach to complete the book. Brother Aidan is the mentor, while Aisling is a supernatural ally—not the boy who completes the manuscript.