Oppenheimer was more the point man on it, indeed, buy it was Einstein who wrote the letter stating how important it was for the US to get the bomb made before the Nazis could.
[i]t was Einstein who wrote the letter stating how important it was for the US to get the bomb made before the Nazis could.
Actually, it was written by Leo Szilard, but went out under Einstein’s name. (Check out “The Making of the Atomic Bomb” by Richard Rhodes).