Billy Katagiri (ビリー・カタギリ, Birī Katagiri) is a fictional character in the anime, Mobile Suit Gundam 00. Billy was an engineer working for the Mobile Suit Warehouse and Development (MSWΛD), who got transferred into the Overflags during the start of Celestial Being's armed intevention. Five years later, he joined the A-Laws to fight against Celestial Being. He later helped the Innovators develop their mobile suit prior the Battle of Lagrange 2. After the defeat of the A-Laws and Innovators, Billy joined the Earth Sphere Federation as one of their chief military technologist.