Another small tidbit of lost computer history: The first person who lost a game to a computer was an unnamed Los Alamos laboratory assistant who lost a game of simplified chess against a computer program in 1956 [1]. The assistant's name seems to be lost to time.
Already in 1950 in the Canadian National Exhibition, the visitors lost (it seems) most of their games of tic-tac-toe against Bertie the Brain, which was a custom computer: https://en.wikipedia.org/wiki/Bertie_the_Brain#Gameplay
Excellent! Upon further digging, I found out that a chess grandmaster, one Savielly Tartakower, was defeated by El Ajedrecista [1], a machine that could play chess endgames. This was 1951, so before the Los Alamos lab assistant, but a bit after the defeat of customers by Bertie the Brain.
The Ajedrecista had been around since 1912, so I would expect somebody must have been defeated by it in the years before 1951.