Thaddeus is a scientist, who managed, along with others, revive Amaura and Aurorus from fossils. He led a tour with Ash, Serena, Clemont, Bonnie, and Alexa. Team Rocket, who spied on them, stole Amaura and Aurorus. Thaddeus worried, for in warm weather, Amaura might get sick. When the heroes defeated Team Rocket, Thaddeus arrived with a truck to transport Amaura and Aurorus back to the lab, where the cold climate suited them.