Rainer Casper began his career at the Schauspiel Köln. He then worked as head of lighting at the Schauspiel Hannover, Central Theater in Leipzig and Volksbühne Berlin, where his long-term collaboration with Frank Castorf began. There he was responsible for the lights for many productions including Erniedrigte und Beleidigte, which was invited to the Theatertreffen festival in 2002. He's worked with directors such as Nicolas Stemann and Sebastian Hartmann at venues including the Nationaltheater Oslo, HAU Berlin and Burgtheater Wien. At the Wiener Festwochen in 2008, he created the lighting design for Frank Castorf's production of Wolfgang Rihm's opera Jacob Lenz. He currently works at the Münchner Kammerspiele. In the 2020/2021 season of the Maxim Gorki Theater, Casper is designing the lighting for Ersan Mondtag's production It's going to get worse.