So a little bit longer version of the story: Eckert and Mauchly had designed the architecture. Herman Goldstine, the military liaison of the ENIAC project, and

So a little bit longer version of the story: Eckert and Mauchly had designed the architecture. Herman Goldstine, the military liaison of the ENIAC project, and something of a social climber, sought out von Neumann to see if he was interested. von Neumann was, and came to a lot of design meetings and made contributions about what the instruction set should be. Then when he was heading out to Los Alamos on a trip, he had some downtime during travel and wrote up the design for the group. Goldstine typed it up and circulated it with just von Neumann's name on it. It is a point of discredit to von Neumann that he did not disavow the naming of the architecture. Funnily, Goldstine's wife was one of the early programmers and well respected in that area. Goldstine himself made no significant contributions to computing.