The Ratman is a common myth in Grand Theft Auto IV. It's existence is currently unproven, but many of GTA 4's fans have argumented whether it does or does not. Most pictures that tend to surface on the internet are real in-game clips, but because there is currently no active mod for the Ratman, they are most likely just photoshopped images. Some pictures are also just the result of a common mistake, such as the mistaking of homeless people in the subway for the Ratman.
At a convention, a GTA CEO stated that "There currently is no Ratman, but it is possible that in games like these with many graphics, some thing could erupt and take on a role of it's own".
The Ratman is supposedly found in the Subway and on some occasions he has been sighted roaming around some areas of Charge Island. Also, a shadowy figure is rumored to be seen some times in the museum at 00:00 in multiplayer.If you do try to look for him at the museum look for it when its foggy