Sonic Team
The initial team formed in 1990 and was composed of developers from Sega's Consumer Development division, including programmer Yuji Naka, artist Naoto Ohshima, and level designer Hirokazu Yasuhara. The team took the name Sonic Team in 1991 with the release of "Sonic the Hedgehog" for the Sega Genesis. The game was a major success that contributed to millions of Genesis sales. The next "Sonic" games were developed by Naka and Yasuhara in America at Sega Technical Institute, while Ohshima worked on "Sonic CD" in Japan. Naka returned to Japan in late 1994 to become the head of CS3, later renamed R&D #8. During this time, the division took on the Sonic Team brand but developed games that do not feature Sonic, such as "Nights into Dreams" (1996) and "Burning Rangers" (1998).
Ristar
Back in late 1994, Sega was originally pitching "Ristar" to be the successor of Sonic the Hedgehog. However, the game never received a ton of exposure or sales, mainly due to being released just three months prior to the Sega Saturn, Sega's successor to the Genesis, overshadowing it. In a 1994 "Electronic Gaming Monthly" interview, Sega marketing staff Lisa Best and Terry Tang claimed "Ristar" was not designed by the same "Sonic" programming team, although much of the game's staff would later go on to create "Nights Into Dreams" for the Saturn, the next game to be officially credited to Sonic Team. This, along with "Ristar's" inclusion in a number of "Sonic" themed compilations and re-releases in subsequent year, would lead game journalists to retroactively label the game as being developed by Sonic Team.