A Keep warden is a protector of the Wizard's Keep. They are to be the non-magical protection of the Keep.
In the book, Naked Empire, First Wizard Zeddicus Zu'l Zorander and Sorceress Adie are in the Wizard's Keep when it is attacked by those who are pristinely ungifted. Following the attack, the pair are captured and taken away from the Keep, leaving it defenseless. Following their forced departure, many things are taken from the Keep.
After Zedd and Adie are rescued from the Imperial Order camp, Zedd speaks with the former boundary warden Chase about helping protect the Keep. Chase reluctantly agrees and coined the term Keep Warden in reference to his former position.
Chase and Friedrich Gilder are named the first Keep wardens.