Police detective Yokoda is brutally murdered, and most of his body is resurrected into a cyborg by a Professor Genius; the resulting crimefighting machine is called Tobor, the 8th Man (presumably models 1 thru 7 didn't 'take'). In his new semi-robotic body he has enhanced strength and speed, and can alter his form to resemble others. 8 Man continues to help his city's police department fight crime, and they - along with the Professor - are the only ones who know the secret of his creation. No superhero is any good without some decent nemeses, and 8 Man's included the mob organization called Intercrime and such baddies as Dr. Demon and The Armored Man.
If parts of 8 Man's origin sound familiar, it's because some of it was used in the storyline of the American 80's sci-fi actioner Robocop, starring Peter Weller. In 1992, a live-action 8 Man movie was produced, and the next year, a new TV series called 8 Man After appeared. Both were 'updated' versions of the original character for modern audiences - i.e., attempted to be grittier, more emotionally overwrought, etc.