Yuji Naka, of Sega's Sonic Team, is a very, very talented games designer. He was responsible most directly with the original Sonic, Sonic CD, Burning Rangers and NiGHTS. The 16-bit Sonic sequels were largely put together by other teams in the US as well as Japan. (Similar to Streets of Rage 3).
More recently he has been involved in the design and development of the Sonic Adventure and Phantasy Star Online series of games (both originating on the Dreamcast, but now being ported to the current generation of consoles starting with the Nintendo Gamecube.)