The guy responsible for Final Fantasy, in the beginning, and to date the executive producer of each and every game in the Final Fantasy series proper. As one might expect, he works for Square Co. Ltd., based in Japan, although a good amount of his work is done at Square Honolulu. He also had a hand in other non-Final Fantasy games, such as Chrono Trigger and its sequel/continuation/whatever Chrono Cross. His contribution to almost every Square game that had any considerable success led him to become vice president of the company, although he stepped down and accepted a lower position after Square posted a net loss in profits during the 2000 fiscal year (apparently, that's some kind of Japanese business custom. Go figure.)
His most recent exploits include Final Fantasy: The Sprits Within, the not-quite-successful Hollywood-produced computer-animated feature film, as well as the latest in the ever-popular marquee series, Final Fantasy X. Surprisingly enough, his current projects likely include Final Fantasy XI and Final Fantasy XII (which has been announced, but no details or even a target platform have been released) which is the first Final Fantasy game which he will not be the exclusive producer of. There is also a rumour of a new game in the Chrono Trigger franchise, and of course he could be working to some extent on any RPG in development at Square.
Sakaguchi has shaped the direction of the RPG genre, and Final Fantasy has always been one of the primary selling points of any console. He certainly has had a lasting impact on the gaming industry.
As always, /msg me with corrections or additions...