The 2010 South Korean horror film I Saw The Devil is a modern twist on this classic tale. In this version, the monster exists first, brutally killing a woman early in the film. The twist is that the cop going after hiim turns himself into another monster, playing a deadly game of cat and mouse with this horrible killer.
The film is really, really intense and quite graphic, so I wouldn't recommend it for the newcomer to the genre. The monsters in the film are all human and there are a lot of very disturbing images throughout.
For me the most shocking thing about the film was how it took this classic story of a man creating something that should not be and having the thing that should not be turn a man into another thing like itself.
Although it was a harrowing experience the film was definitely worth checking out, story and character are so often under-used in horror.