He is originally Chinese, and the Chinese pronunciation is Wu Qingyuan (i.e. his name is written the same in Chinese and Japanese, with the characters 吳清源, but the Japanese pronunciation is different).

The character in his name is not the same as the one for the game.

Interestingly, both Japanese 'go' and Chinese 'wu' can have the meaning 'five', but that is yet another different character :)

Nomen est Omen indeed. His Chinese name is Wu Qingyuan, and it just turns out that "Go" is how you pronounce his last name in Japanese.