Thaddeus (Japanese: タケダ Takeda) is a character of the day who appeared in Coming Back into the Cold!. He is a researcher working at the Ambrette Town Fossil Lab.
Thaddeus welcomed Alexa and Ash and his friends in the Fossil Lab, as Alexa had requested an interview. He showed them around the main room with many Fossils on display. After this he brought them to a special room and gave them winter coats before they entered it. This room was a special "freezer room" where an Amaura and an Aurorus the lab had revived earlier lived. Thaddeus explained to the group how an excavation group had found the Fossils of Amaura and Aurorus high up in the north of the Kalos region and brought them to the Fossil Lab where they were revived.
Later, when they had exited the freezer room, Team Rocket broke in and managed to steal Amaura. This wasn't left unnoticed and Thaddeus and the group quickly rushed to the scene. Team Rocket had already left with their truck however. Thaddeus mentioned how Amaura wouldn't be able to hold on for a very long time, as it is weak to heat. If they wouldn't save it quickly, it would be in mortal danger. Alexa and the group decided to go after it with the help of Aurorus, and Alexa instructed Thaddeus to make preparations for transporting Amaura might they find it.
Later, when the group and Aurorus found and defeated Team Rocket and saved Amaura, Thaddeus arrived with a large truck to safely transport Amaura and Aurorus back to the lab. Back in the freezer room, Thaddeus informed the group Amaura was fine.