As nuclear tensions rise worldwide and the war in Ukraine reshapes global security, Rafael Grossi stands at the centre of the world’s most dangerous calculations. The director general of the International Atomic Energy Agency discusses the risks of escalation, the limits of diplomacy and the credibility of nuclear oversight. Now a declared candidate for United Nations secretary-general, Grossi also addresses calls to reform what critics describe as a weakened institution. Can the UN still prevent conflict, or is the global order fragmenting beyond repair?