Depends on definition. Three key milestones:
Magnavox Odyssey (1972) — Designed by Ralph Baer. Cartridge-based (circuit jumpers), no CPU, analog circuitry, plastic screen overlays for color. 28 games (12 included). ~350,000 sold.
"Brown Box" (1968–1970) — Baer's lab prototype. Ping-pong, volleyball, light-gun. Demonstrated to Magnavox → Odyssey. Displayed at Smithsonian.
"Spacewar!" (1962) — PDP-1 mainframe (MIT). Two ships, gravity star. Not a consumer device.
"The Game" (1972) — PDP-11 program by Greg Thompson. Early networked multiplayer. Still a mainframe program.
Atari Pong (1975) came later. Odyssey = Generation Zero.