John Barleycorn is one of the citizens of Smalltown. He's actually a hero to the Lilliputians.
John Barleycorn was originally Johnny Bullhorn. Upon hearing that Thumbelina was born from a magic barleycorn and knowing that Smalltown needed women, he volunteered to go find the jar of magic barleycorns. Along with Commander Arrow of the Farm Air Patrol, he headed to the Homelands.
They went to the house of the witch created the barleycorns to find it empty. A grasshopper named Mustard Pot Pete told them the barleycorns were in a nearby tower. A Mister Grandours was guarding the tower, but he disliked the Adversary so he returned to Fabletown with Johnny.
There was a great celebration following Johnny's return. The barleycorn's were planted and soon there were weddings. After that adventure, Johnny Bullhorn became John Barleycorn. The magic barleycorns were taken to the business office and it became tradition for young men in Smalltown to try to steal one.
John Barleycorn is based on a folk song of the same name. In the song, John Barleycorn is the personification of barley. The song describes the various stages of barley cultivation as various indignities John Barleycorn must go through.