
Sadaharu Oh is pronounced "SAH-dah-hah-roo Oh." In Japanese his name is written 王 貞治 (Oh Sadaharu).
No. Sadaharu Oh spent his professional playing career in Japan with the Yomiuri Giants and built his record in Nippon Professional Baseball (NPB).
Yes. He is widely recognized as one of Japan’s greatest players and is honored in Japanese baseball history, including recognition in Japan’s baseball hall of fame.
A good place to start is the dedicated Wikipedia page listed in the reference links for photos, career details, and further reading.