Answer: Japanese hammer thrower Shigenobu Murofushi.
Shigenobu first won the Asian Games hammer throw competitions in 1970, then successfully defended it in 1974, 1978, 1982 and 1986 for a total of 5 Asian Games editions. Not only that, in 1966, he was the silver medalist behind compatriot Takeo Sugawara.
Incidentally, he has a son who is not just an Asian Games champion himself (1998 and 2002), but an Olympic (2004) and World Champion (2011) at the hammer, Koji Murofushi.
Source: GBR athletics.com, Wikipedia