Short answers, pulled from the story.
The Game Boy was released in Japan on the 21st of April, 1989, in North America on the 31st of July, 1989, and in Europe on the 28th of September, 1990. Its entire initial Japanese production run of 300,000 units sold out within two weeks.
The Game Boy and Game Boy Color together sold a combined 118.69 million units worldwide by the time of discontinuation in 2003. This broke down to 32.47 million in Japan, 44.06 million in the Americas, and 42.16 million in other regions.
The Game Boy was designed by Nintendo Research and Development 1 under division director Gunpei Yokoi and assistant director Satoru Okada. The project was internally codenamed Dot Matrix Game, reflected in the console's official model number DMG-01.
Nintendo's design team chose a monochrome display following Gunpei Yokoi's philosophy of using mature, low-cost technology over cutting-edge alternatives. Color screens cost more and consumed significantly more power, a tradeoff that left competing color handhelds with notably short battery lives while the Game Boy could run up to 30 hours on four AA batteries.
Henk Rogers, who held the rights to Tetris, persuaded Nintendo of America president Minoru Arakawa that Mario appealed primarily to young boys while Tetris appealed to everyone. Tetris was bundled with the Game Boy in every region except Japan, and it went on to ship more than 35 million copies, making it the bestselling single game on the platform.
The bestselling franchise on the Game Boy was Pokemon Red, Blue, and Yellow, the first installments of the Pokemon video game series, which sold more than 46 million copies combined. The Game Link Cable that enabled Pokemon's battle and trade mechanics was personally developed by Satoru Okada.