If you ask someone to name the very first videogame, they might mention Pac-Man (1980), Space Invaders (1978), or maybe even Pong (1972). But to find the granddaddy of them all, you have to go back another 20 years.
If you define a videogame as a computer program that sends signals to a television or monitor, then the accolade goes to A.S. Douglas who created a Tic-Tac-Toe game while studying for his PhD at the University of Cambridge in 1952. Designed to run on an EDSAC vacuum-tube computer, the game displayed on a 35×16 pixel display and was sophisticated enough to beat most human opponents.
Wikipedia: First Video Game