That is generally reckoned to be the Sumerians, but actually we don't know. There was a prehistoric "stone axe" factory at Olorgesailie in Kenya that appears to have been inhabited for the greater part of 3 million years (longer than Homo Sapiens has walked the earth) where numbers must have been important to the manufacturers, repairers and "sellers". It is safe to assume that some sort of numbering/counting system was used by Homo Erectus, the probable inhabitants of the site.
