Yeah, Thomas Ian Griffith (Terry Silver actor) is an official martial arts guy. You can easily tell way back in TKK3 when he's doing his kata and shyt. His kicks are still quite clean and solid at his what...60+ years of age. He the most official karate/ma main cast member throughout all of the movies and show (tho the Mike Barnes actor was also of official karate ilk), aside from Jackie Chan, if you counting that movie...which none of us do.
Funny how duke completely gave up all acting and everything like over 20 years ago and they were able to pull him back in for this joint and he pulls it off effortless and bringing new dimensions to the character to boot.
dude did his own stunts from what it looks like....from his imdb
Trained Tae Kwon Do under Master Jun Chong. Besides Tae Kwon Do and Kenpo Karate, he's also trained in kickboxing, wrestling and fencing. He also has experience in stage combat.