Short answers, pulled from the story.
The Sega Genesis launched officially in September 1989 in North America, though a small number of units reached retailers in New York and Los Angeles in late August 1989. In Japan it had been released earlier, on the 29th of October 1988, under the name Mega Drive.
The Genesis hardware was designed by an R&D team led by Masami Ishikawa and supervised by Hideki Sato. The console's physical appearance was designed by a separate team led by Mitsushige Shiraiwa, who drew inspiration from audiophile equipment and automobiles.
Tom Kalinske, CEO of Sega of America, replaced the pack-in game Altered Beast with Sonic the Hedgehog in 1991. Critics praised Sonic as one of the greatest games made at the time, and the Genesis outsold the SNES nearly two to one during the 1991 holiday season. By January 1992, Sega held 65% of the 16-bit console market, the first time Nintendo had not led the market since 1985.
Controversy over Mortal Kombat and Night Trap led to congressional hearings in 1993. Sega created the Videogame Rating Council for its own platforms in response, but after objections from Nintendo and others, the industry came together to form the independent Entertainment Software Rating Board, which Senator Joe Lieberman praised when it was in place for the 1994 holiday season.
Sega sold 30.75 million first-party Genesis units worldwide, including approximately 3.58 million in Japan, roughly 8 million in Europe, and between 18 and 18.5 million in the United States as of June 1997. Tectoy sold an estimated 3 million additional licensed units in Brazil as of 2012.
EA reverse-engineered the Genesis starting in 1989 using a clean-room method, led by Steve Hayes and Jim Nitchals. EA founder Trip Hawkins confronted Sega's Hayao Nakayama the day before the 1990 Consumer Electronics Show and told him EA could run its own licensing program. Sega relented and signed an agreement in June 1990 giving EA the right to approve its own titles and negotiate more favorable royalty rates.