Ultra-Duck (also known as Big Bill Screwloose) was a "superhero" possibly living in the Emerald Hill Zone. Masquerading as a hero more capable of fighting Badniks than Amy Rose and Shortfuse the Cybernik, Big Bill actually worked for Doctor Robotnik. By building old Badniks programmed to lose, Ultra-Duck ensured he was always first on the scene when the Badniks came to attack. His plan was to make civilians lose faith in the Freedom Fighters for getting to danger areas so slowly. His plan worked, with Ultra-Duck becoming the Sunshine Valley Zone's favourite hero.
Screwloose's plan came unstuck when real Badniks came to attack the Emerald Hill Zone. Ultra-Duck made a run for it, leaving Amy and Shortfuse to deal with the attackers. Tekno the Canary made sure Bill didn't get away, before removing his mask and divulging his rotten backstory to everyone else.
Shortly after his villanous escapades, Screwloose became a street cleaner. The memory of Ultra-Duck quickly fell out of most people's minds, and he never joined the League of Super-Evil Villains.
He showed up in the "New To STC?" feature, together with other failed supervillains. Unlike the rest, he didn't join the League of Super-Evil Villains.