Mentor of Arisia is a fictional alien from the planet Arisia in Edward Elmer "Doc" Smith's Lensman series. Mentor is actually a fusion of the four Arisian minds (Drounli, Kriedigan, Nedanillor, and Brolenteen) known to Arisians as The Moulders of Civilization, and were individually responsible for protecting the nascent civilizations of Sol III, Velantia III, Rigel IV, and Palain VII from attack by the Eddorians. The collective fusion was the agent who interacted with, and trained, all Lensmen who were sent to Arisia to receive their Lenses.
Mentor "passes into the next plane" of his own volition at the completion of the Eddorian War, telling the Children of the Lens that they were ready to assume the mantle of the Guardians of Civilization.