Abbot is a narcissist, and so believes that he is more important than others. He prefers that there would be death for all before disgrace for him.
Leon Abbot was against the time-spell at the Battle of Taillte in Hybras, so, with his friend Bludwin, broke the Circle of Warlocks just as they were performing the spell. He and Qweffor, an apprentice warlock, were merged by lava and magic and catapulted to the "near past" (most likely 2001). Abbot retained control of the body, and stole Qweffor's magic.
On Earth, he learned the "secrets" of humans from Minerva Paradizo, who gave him a book and a crossbow to study. Finally, he went back to Hybras in the past at the exact moment that the time-spell was put into effect, then took out the book and the crossbow, claiming to be the demons' savior. He used the magic stolen from Qweffor to mesmerize anyone who challenged him for the throne. Leon Abbot mesmerized Nº1 into removing his silver and transporting him off Hybras.
Nº1, who had been revealed to be a warlock, returned with Holly, Artemis (who had just acquired magic), and Qwan to perform the time spell. Leon Abbot kills all of them except Artemis, but he is able to bring them back by shooting Leon Abbot from the future, stopping him from killing them in the past. This happens because of a time surge occurring because the original time spell is breaking up. At the end of the book, Qweffor takes over Abbot's body and, with Artemis, Holly, Nº1, and Qwan, is able to successfully transport Hybras back to Earth. Abbot's consciousness is subsequently transferred to a guinea pig to stop him from hurting anybody. Warlock interns enjoy throwing miniature swords to the guinea pig and watching it trying (and failing) to pick them up.
Abbot's demon name is N'zall, meaning "little horn" in ancient demon language, a fact that he was always embarrassed by. For this reason, he started to call himself Leon Abbot, after the general in the book he brought back, Lady Heatherington Smythe's Hedgerow.