From A Wiki of Ice and Fire
|Book||The Sworn Sword (appears)|
Wat, also known as Wat Barleycorn, was a farmer in service to House Osgrey. He had a younger brother, Wet Wat.
Wat was among those that were called by Ser Eustace Osgrey to defend the Osgrey lands after a disagreement over the Chequy Water with House Webber escalated into threats of war. He was given the name "Barleycorn", derived from the crop planted in the town he comes from, in an effort to distinguish him from the other Wats among the forces. He was to be wed the next time the septon came through. His younger brother of the same name was given the name "Wet Wat".
Wat was sent home by Ser Duncan the Tall with the others when Duncan realized that it would be futile to fight.