The international criminal known as Wo Fat is the arch nemesis of the main character on which American action series?

Wo Fat is the arch nemesis of Steve McGarrett. They appeared in the original series "Hawaii Five-O" which ran from 1968 to 1980. McGarrett (Jack Lord) was the head of Hawaii's (fictional) special task force, Five-O. This task force was based on an actual unit that existed under martial law in the 1940s.

Regarding Wo Fat, he was a villain that appeared in eleven episodes of "Hawaii Five-O". He was important enough to be part of the TV-movie pilot and the final episode shot in 1980. The character of Wo Fat evolved from being a master spy for China. Later, he had turned into an extremist Chinese agent working with a hawkish Chinese general. The general opposed peace discussions with the United States in the early 1970s. By the end of the series, Wo Fat had become an international super criminal out for his own interests.

In the end, Wo Fat is arrested and jailed after 12 years as a wanted criminal. However, in his final scene, he smiles and craftily produces a file hidden in his shoe. With the 2010 reboot of "Hawaii Five-0", the character of Wo fat is skillfully and totally re-imagined. But, he remains a criminal and a former agent of the Chinese government (specifically the Ministry of State Security).