This myth has to do with a particular pedestrian found in the game. This ped is a white male, who wears a cowboy hat, a checkered red and black jacket, and denim jeans. His skin ID is 161. This pedestrian commonly spawns in rural areas or in the countrysides around the state, but players have reported that this pedestrian spawns with random weapons, ranging from knives to assault rifles. He is also known to carry a Desert Eagle and a Shotgun, but a few screenshots show him with various assault rifles as well.
This pedestrian normally spawns in rural or countryside areas, but the pedestrian involved with this myth can be found near the two bridges that connect Shady Creeks to Back O' Beyond. The pedestrian is known to attack the player unprovoked and with no warning at all. This myth is very strange because it would be unusual to find pedestrians in very isolated areas like Back O' Beyond.
It was first believed that the pedestrian was just misspawned, but soon rumors began to arise about the ped attacking players unprovoked. The myth then started to gain notoriety, as more and more players made rumors about the Killer Cowboy. Player reports say that your chance to encounter him increases in Stormy-Foggy weather late at night.
Another belief is that the Killer Cowboy could potentially be the creature Rockstar mentioned was somewhere in the woods, also known as the Shady Creeks Creature.
He spawns at an increased rate after the BGLUAWML cheat code has been entered.