Before the anime, before Adventure, before the card games and the arena, there was a small gray keychain with a tiny screen. The whole Digimon world started with the Digital Monster virtual pet, launched in Japan on June 26, 1997, and in North America on December 5, 1997. (This is an unofficial fan post from the Digital Colosseum community, not an official Bandai source.)
A "boy's Tamagotchi"
The device was built by WiZ and Bandai as the masculine counterpart to the Tamagotchi. Bandai had found huge success with Tamagotchi, but that toy skewed heavily toward girls. The Digital Monster was designed for boys aged eight and up: tougher, harder to raise, and built around one thing Tamagotchi didn't do — battling.
The team behind it included Makoto Kitagawara and Kenji Watanabe of WiZ, plus Ayumu Horimura of Bandai as supervisor. Early on the project went by the codename "Otokotchi" (a nod to the "boy's Tamagotchi" idea), then "Capsule Zaurus," before the team settled on "Digital Monster" when they worried "Capsule Zaurus" might clash with another company's trademark.
Monster designer Kenji Watanabe drew from American comics like Spawn, and from artists Simon Bisley and Mike Mignola, to give the creatures their dark, muscular look. The first two Digimon he ever designed were Tyranomon and Agumon. Today the franchise is credited to the collective pen name "Akiyoshi Hongo," which covers the many people involved rather than a single creator.
How it played
Like a virtual pet, the Digital Monster constantly demands attention. You hatch an egg, then raise the creature as it grows day by day: feed it meat and a protein pill, train it, clean up its droppings, heal sickness and injuries, and switch the light off at bedtime. Ignore a call, leave the poop, or leave the light on, and you stack "care mistakes" — and care mistakes quietly steer which form your Digimon becomes.
Two friends could link their devices by touching the metal contacts together, connecting the keychains to make their Digimon fight. Battle performance and the quality of your care together decide which evolution path you end up on, climbing through several stages from a baby up to a fully evolved "Perfect" form. In the original release the roster held about 14 Digimon across roughly five stages, so two well-raised partners could wind up with very different monsters.
Where it went
A second generation of virtual pets followed in 1998, and then came the Pendulum line, which added the higher "Ultimate" stage and Jogress, a feature that let two compatible Digimon fuse into a stronger one. From there the franchise kept snowballing into the 1999 anime Digimon Adventure and everything that came after — video games, cards, comics, and decades of new seasons.
Twenty years later, on June 26, 2017, Bandai re-released the device as the Digital Monster ver. 20th in its original brown and gray shells, a faithful nod to the little keychain that started it all. If you grew up alongside Tamagotchi, you can see how the two worlds connect over at our sister hub, https://tama.fdhcl.com — but make no mistake, the Digital Monster was its own beast, and it roared first.