Who invented graffiti?

It wasnt really invented per se....basically whoever it is that wants to express themselves. Phetus, who is an all time favorite of mine and is the mastermind of elitegudz.com, has been on the scene for over 20 years. His graffiti is in true art form

Added: Considering that paintings on the walls of caves have been dated back to prehistoric times I think it's safe to say that it has been around ever since mankind began to walk upright.