In 1983, he and Michael Weikath founded Helloween, where he was guitarist and singer until Michael Kiske took over the microphone for the albums Keeper of the Seven Keys Part 1 and Keeper of the Seven Keys Part 2.
Godine 1984., Hansen i Michael Weikath osnovali su sastav Helloween, u kome je Hansen svirao gitaru i pjevao sve dok Michael Kiske nije preuzeo mikrofon na albumima Keeper of the Seven Keys, Part 1 i Keeper of the Seven Keys, Part 2.