Eliezer Yudkowsky's fan fiction reimagines the Harry Potter universe with Harry raised by a scientist stepfather who taught him the methods of science and rational thinking. When Harry discovers he is a wizard, he approaches the magical world as a scientist would, systematically testing the rules of magic and questioning assumptions that wizards take for granted. The story uses the Harry Potter setting to explore concepts from cognitive science, economics, and artificial intelligence research, with Harry applying Bayesian reasoning and experimental method to magical problems. Yudkowsky, an AI researcher who founded the Machine Intelligence Research Institute, created the work to introduce rationalist concepts in accessible, entertaining form. The story diverges significantly from canon, developing new plot lines and reimagining characters while maintaining the magical setting. Harry's friendship with Hermione becomes a meeting of intellectual equals, while his conflict with Voldemort takes on new dimensions as both are portrayed as rational actors pursuing coherent goals. The work has developed a substantial following among those interested in rationality, effective altruism, and artificial intelligence safety, while also appealing to readers who simply enjoy clever plotting and inventive world-building.