Quantum mechanics continues to beguile scholars and the public alike, as does the stirring tale of its discovery: during the interwar period, amid the vibrant milieu of Weimar Germany, a collection of liberal, free-thinking physicists, many of whom were Jewish, developed a theory that changed the world. It is thus all the more curious that one of the major architects of this famous theory remains practically unknown: the brilliant German mathematical physicist Pascual Jordan (1902–1980). At only age 24, Jordan, in collaboration with Werner Heisenberg and Max Born, outlined the fundamentals of quantum theory as we now know them. Yet Jordan is overlooked today due to his Nazi-era writings that praised Hitler’s regime; an unrepentant fascist hardly fits into the usual heroic narrative of scientific triumph. But the omission of Jordan has left a lacuna; he almost certainly deserved a Nobel Prize for his scientific contributions and he trained an entire generation of West German physicists after the war. Moreover, it is historically significant that one of the talented quantum pioneers saw no apparent contradiction in joining the Nazi Party. This dissertation fills this gap, presenting the first full account of Jordan’s complicated and contradictory twentieth century life and adding necessary nuance to the traditionally gallant story of quantum mechanics. Using newly discovered sources from over twenty different archives, The Forgotten Founder of Quantum Mechanics makes four major historiographical interventions. First, it demonstrates that actions taken long after Hitler’s death often dictated who is collectively remembered as an “unapologetic Nazi.” Without relativizing his Nazi-era actions, this dissertation shows that Jordan came to be remembered exclusively as a remorseless fascist not, as has been thought, exclusively because of his pro-Nazi statements during the Third Reich, but in large part due to his decision to reenter politics in the late 1950s as a Cold Warrior in postwar West Germany. Second, this dissertation refutes the common misconception that modern science can only function properly in a democracy. During World War II, Jordan in Nazi Germany outlined a vision of science on an industrial scale, strikingly similar to that which developed in the United States after the war. But Jordan’s version of “big science” had a Nazi veneer, envisioning a network of research institutes across Europe under German control. Though Nazi authorities proved uninterested in his plan, that Jordan developed it under such an autocracy demonstrates that there is nothing inherently democratic about big science. The failure of Jordan’s attempt to found a “Nazified” version of “big science” leads to this dissertation’s third intervention, namely, the proposal of a new model of analysis for historians of the Nazi regime—and other authoritarian systems. This is namely that of the “failed collaborator,” as I characterize Jordan; for despite all his attempts to convince the regime that science was worthy of lavish financial support, the Nazis remained indifferent to Jordan’s pleas. Finally, this dissertation shows that Jordan’s stutter severely hampered his career prospects. Because of this invisible disability, he was denied opportunities to build his reputation and further his career—even well before his political radicalization in the early 1930s. I argue that Jordan’s stutter was a crucial factor in why he never achieved the same level of recognition as his more famous colleagues—and why he never won the Nobel Prize. Ultimately, this dissertation argues that Jordan’s life should be remembered precisely for the reasons why it has been forgotten, as those reasons reveal much about both German history and the history of modern science.