Willem Viceroy III is Hannibal McFist's mad scientist as well as being the secondary antagonist. He is the evil scientist but rather refined madman responsible for all of the bizarre robots attacking Randy. As McFist's chief mad scientist, Viceroy doesn’t really care about money or power; he just wants everyone to appreciate his genius.
Very dry-humored and sarcastic, as well as refined and somewhat effeminate, Viceroy works hard to create deadly robots and monsters to destroy the Ninja. He gets frustrated that McFist usually claims the creations or schemes were his idea or blames him for something that was actually McFist's fault. When Viceroy attended Mad Scientist University, he managed to get fellow rival Jerry Driscoll caught for making a doomsday device in order to become valedictorian and get attention.
In the episode, "Monster Dump", it's revealed that Viceroy has a pet amoeba named "Nicholas". He went down into the volcano to get him, showing that he cares very much about his pet. When falling into the volcano, he activated an inflatable lab coat which he was wearing on his regular one, saving him from injury. When Randy rescued Nicholas, Viceroy promised to take a vacation from helping McFist destroy the Norrisville Ninja. He was seen at the end of the episode in Provence, riding his scooter with Nicholas.