Iannis Xenakis (1922–2001) is one of the most protean creators of the past century: trained as a civil engineer, turned architect under Le Corbusier, composer of music that deliberately turned its back on tradition, pioneer in electronic and computer-generated music, and trailblazer for the philosophy and realization of trans-disciplinary art. In addition, his past as an active Resistance fighter and leader during the Greek Civil war and World War II left indelible traces not only on his handsome face but also on his psyche, shifting his personal battle into the field of ideas. This talk aims to show how this “ancient Greek born in the XXth century” has transformed/influenced the evolution of music through his integration of subjects generally considered outside of composition (including mathematics) into his works. An ulterior motive of this talk is to bring a human face to the author of titles such Formalized Music and Arts/Sciences: Alloys by one of his closest collaborators during the last twenty years of his life.