Arnolde becomes the first centaur king for a brief time in Night Mare, at the age of ninety-eight. During his reign, he declares Sorceresses are merely female Magicians, and therefore eligible to serve as Kings of Xanth.
In Golem in the Gears, he reveals he has discovered he can create an aisle of non-magic in Xanth while carrying reverse wood.
In Roc and a Hard Place, he is found to have moved into the Region of Madness with his friend Ichabod, which helps sustain his life due to the concentrated magic there, but the two leave the Region temporarily in order to help Demoness Metria travel to Mundania (without his magic aisle, she would not be able to exist there).
The true nature of Arnolde's talent is finally revealed in Currant Events: though he long believed it was a concentration of magic within his body that had generated the aisle, he actually has the ability to translate gravity (the magic of the Demon E(A/R)th) into Xanth magic in an aisle around him. After he and Clio, the Muse of History, persuade David Baldwin to let Demon E(A/R)th develop a connection with him, E(A/R)th enhances Arnolde's talent by lending him more energy.