In 2013, a Polish YouTuber called gtamythhunter16a found a creature in the Cedar Grove Woods. The creature appears to look black and its face is blurred. The player then shot him, and the creature disappeared, possibly due to a script. The creature's origin is unclear and it is unknown whether if it's a biological creature or not.
The possibilities are, that it may be a unique pedestrian texture, which was meant to be kept in the beta, but was later removed. Then, in the final release, it could have been a failed or accidental spawn. It is also possible that the pedestrian model was not properly textured, so it was removed and kept in the woods to hide it, thinking that no one could find it.