As we mark the 30th anniversary of the Tadić interlocutory appeal on jurisdiction of the International Criminal Tribunal for the former Yugoslavia, this special contribution commemorates the moment by looking at Antonio Cassese’s impact on international law, with a particular focus on his understanding of his own methodology, which could be described as ‘critical positivism’ and executed by a ‘judicious reformer’. ‘The Man in a Case’ in the title is a reference to a famous short story by Anton Chekov, a piece that Cassese particularly liked. With a wry smile, he used to say that lawyers who adhered to strict legal positivism risked becoming like the character in the story, Belikov, who lived a solitary existence and adhered strictly to a rigid set of rules and principles, building metaphorical walls around himself like a ‘man in a case’. Although Cassese recognized the safeguarding role that legal positivism can play in shielding legal discourse from ideological manipulation, he cautioned against the potential of pure positivism to put distance between lawyers and the socio-political challenges he thought we should be addressing in the real world. In his approach to law, as a scholar, a judge, and a practitioner, Cassese sought to balance methodological rigour with principled engagement. He emphasized the imperative for jurists to avoid becoming mere instruments of power and strove to maintain a delicate equilibrium between adherence to legal principles and active participation in moral and political discourse. In essence, Cassese’s approach sought to harness the protective function of legal positivism to his need to engage his moral and political commitments.