Who made the first nuclear bomb made?

The United States, with its activities through the Manhattan Project in WW2, produced the first nuclear weapons. There were thousands of people on this project, from my grandfather working as a general construction worker at Hanford and totally baffled at the tons of perfectly good equipment the army kept dumping in trenches and burying (he was still baffled when I was a kid in the 1960s and it had long been publicly announced that Hanford had made the plutonium for the Nagasaki bomb), to J. R. Oppenheimer and Leslie R. Groves that managed the project.

By the end of Operation Crossroads in the summer of 1946 at Bikini Atoll in the Pacific, we had built a grand total of 9 devices, detonated 5 of them, leaving only 4 in "stockpile".