Kernel
Oppenheimer is not the greatest physicist of his generation; he is the figure who, by improbable temperamental fit, can manage a collection of greater physicists. The 27-month run of Los Alamos under his direction is the most successful crash R&D program in history. His subsequent 1954 security-clearance revocation is the United States' clearest signal that its own technical class can be disciplined by political authority.
Contribution
Operational management of the Manhattan Project at Los Alamos. The institutional template that became Argonne, Oak Ridge, Brookhaven, Livermore. His postwar role chairing the General Advisory Committee of the AEC. The Bhagavad Gita reference ("Now I am become Death") that gives the era its literary moment.
Lineage
Harvard, Cambridge (briefly, unhappily, with Rutherford), Göttingen with Born. Returned to Berkeley as the de facto leader of American theoretical physics in the 1930s. Recruited by Groves for Los Alamos. The 1954 hearing strips his clearance; the 2022 declassification confirms the hearing was politically motivated.
Civilization-scale significance
The civilizational figure of the modern scientist-administrator. His career arc is the founding narrative of every research-policy debate since.