Professor E. Gadd is an elderly man, with hair that has left him with only a white tuft running up in a spike. He wears large glasses, with rings on the lenses, and appears to have only one tooth. He wears a white lab coat over a red top.
A brilliant scientist who once lived near Thwomp Volcano, he is known to have helped Mario and Luigi when they journeyed through time. After this event, he began his research on ghosts, and moved into the Boo Woods; there, he once again came to the aid of Luigi when the plumber won a ghost-infested mansion. He has invented a number of devices over the years, and now seeks information on the dark clones running rampant in The Void.
Professor E. Gadd enlists the help of both Luigi and the Avatar in order to hunt down Dark Luigi and learn some information on what exactly all of the dark clones really are.
Mario offers three quests, which are Investigate the Shadow Double!, in which he tasks players with hunting down Dark Luigi, Boo Infestiation, which has the player defeat 10 Boos and 5 Pink Boos, and Dark Research: Mushroom Kingdom, where he asks the player to hunt down each of the more general dark clones around the Mushroom Kingdom.