Risho is the martial arts expert of Ordon Village. He offers to teach Link how to use martial arts, however first Link needs to bring him some Herbal Tea from Hateno Village before he will teach anyone. Following completing that task, Link receives Risho's first lesson. Rakib also sends Link to Master Risho if they haven't learnt the first lesson from him yet.
NOTE: Martial arts is not currently implemented as of 1.9.10