From Sega Retro
Another pivotal name in the early years of Sonic, Hirokazu Yasuhara (安原 広和) was the original game and level designer. He was probably the most actively involved in the early development of the series, and remained one of the chief map designers all the way through Sonic R in 1997. He even had a hand in the design of the shelved Sonic X-treme. In 2002, Yasuhara left Sega and joined fellow former members of the Sega Technical Institute at Naughty Dog, where he worked on the Jak & Daxter series as well as the first installment of Uncharted.
In 2008, Yasuhara departed Naughty Dog to take up a job at Namco-Bandai America, where he's said to be working with some past colleagues. According to a Gamasutra report, he is currently at work on an upcoming Pac-Man title, targeted for a 2010 release (the character's 30th anniversary).
In 2012, Yasuhara was hired by Nintendo Software Technology Corporation, a US-based division of the company of the same name best known for developing the Mario vs. Donkey Kong games, as well as Metroid Prime Hunters.
"I was opposed to [Sega's] decision to create games that use 'Sonic-something' so that they can sell it easily. I wanted to make good games, not any games that used the Sonic character in a haphazard way."