Class 1 overseer was a title used by the Hierarchy of the Delta Quadrant. Holders of this title would have broad access to places such as the Hierarchy Central Command and to a wide amount of tactical information.
In 2378, Zet attempted to disguise The Doctor as a Class 1 overseer so he could infiltrate the Central Command's Surveillance Complex and steal tactical information, which Zet could then sell at a great profit. The Doctor's rescue by USS Voyager personnel, however, prevented that from taking place. (VOY: "Renaissance Man")