South Korean film industry is one of the top 5 film industries in the whole world! It is astonishing and beautiful because of great actors, great actresses and, of course, because of brilliant and visionary directors & screenwriters.
I listed 45 names here, most of them also being screenwriters. The first six listed here are among the 100 directors of all time and I think my conclusions are objective!
My basic criterion was that they must have made at least 2 great (or very good) films, and the majority of them have made even more than two.
My other lists:
Best South Korean Actors
Most Handsome South Korean Actors
Most Prettiest South Korean Actresses
Best South Korean Actresses