Aegis was originally a Soul Weaver who studied in Edelia, the School of Soul Weaving many years ago. While on a mission in the Northlands with other Soul Weavers, one of the Soul Weavers stepped onto thin ice and fell into the water. Aegis jumped in to save him and succeeded, but the Soul Weaver then pushed him back into the ice cold water and he drowned. He was later bonded with the Hero of Lore when the Hero quested to become a Soul Weaver.
Between Book 2 and 3, the Hero was stuck in ice for many years, and due to Aegis being a Spirit of Ice and being bonded to the hero, he became much stronger.