The first known South Korean monster film, Pulgasari was released in 1962. The only known piece of media dealing with the movie is the poster, as it seems to have gone missing almost immediately after it was released.
The existence of the film is often debated, as the poster may be a hoax, but since there has been no evidence either way it can only be assumed that it was lost very quickly. As most South Korean monster films are very rare with few releases within their own country and none outside, there is no way to tell if this is a real movie.
Interestingly, if this movie was real, the North Korean movie of the same name would be a remake, and could give hints to what the original movie was like.
The Korean film Archive information on the film (notice the run time of 0 min)
An article discussing the subject Retrieved March 28, 2007