Marcus McDilda. I would note that there isn't really any evidence that I have seen that his false testimony influenced the Japanese high command in any big way; it's one of these things that is sometimes invoked in a loose way, but is not a serious part of the discussion of why the Japanese high command decided to surrender when they did. (Aside from it being very clear that someone like McDilda would have not know the US production numbers, it is also the case that it would beggar the imagination that the US would wait to have 100 atomic bombs before using one of them.)

The appeal of this kind of story is interesting to me, because it always comes up in a specific context, e.g., both justifying the atomic bombs AND showing the plucky cleverness of American GIs, etc. It's the kind of "answer" to the question ("why did the Japanese surrender?") that certain Americans in particular prefer, over the more complicated ones preferred by historians. (It also sort of assumes the Japanese high command were idiots, which also fits the assumptions of the people who like this kind of answer...)