I'm watching the movie…

…but I've never known anything about the series before. An interesting tidbit from the Wikipedia entry on "The Green Hornet":

He would be accompanied by his similarly masked chauffeur/bodyguard/enforcer, who was also Reid's valet, Kato, initially described as Japanese, and by 1939 as Filipino of Japanese descent.[4] Following the Japanese attack on Pearl Harbor on December 7, 1941, references to a Japanese heritage were dropped.[5]

Specifically, in and up to 1939, in the series' opening narration, Kato was called Britt Reid's "Japanese valet" and from 1940 to '45 he was Reid's "faithful valet." However, by at least the June 1941 episode "Walkout for Profit," about 14 minutes into the episode, Reid specifically noted Kato having a Philippine origin and thus he became Reid's "Filipino valet" as of that point.[6] When the characters were used in the first of a pair of movie serials, the producers had Kato's nationality given as Korean.