Historians tend to specialize in a particular period, an ancient language, or a geographical area. As a result, they often seek answers to their questions within the boundaries of their expertise, despite the rather obvious fact that ideas move across time and space. The concept of the Unknown God can be found in many religions of the past and present. However, experts in Western culture tend to trace its origins to Christian mysticism, Neoplatonism, or Gnosticism. In contrast, Indologists and Egyptologists are well aware that this idea has much deeper roots and is present in Asian and African cultures from more ancient times. Drawing on the valuable work of traditional historians, the historian of ideas takes on the role of a ‘dot-connector.’ In this vein, this article reconstructs the history of Egyptologists’ rediscovery of the Unknown God in ancient Egyptian religion and examines the debate among experts on whether Egyptian religion was monotheistic, henotheistic, or polytheistic. The study also provides some clues about how the concept of the Unknown God reached us through the Greeks and the Hebrews. Thus, this work is not a contribution to Egyptology but rather a contribution to the history of Egyptology within the broader framework of the history of ideas.