He Who Walks Behind the Rows is the name of a demonic fertility spirit that lives among the corn stalks that grow around Gatlin, Nebraska. The god/demon gained influence over the children of Gatlin, who formed a cult worshiping him and massacred the town's adults in 1964. The children established a practice of sacrificing themselves to He Who Walks Behind the Rows once they reach the age of nineteen; the "age of sacrifice" was later lowered to eighteen.
In Children Of The Corn (1984 film) a child named Isaac Chroner was said to be the first who led the children into killing people and their parents to sacrifice them to He Who Walks Behind the Rows. Isaac leads the children and told them once all the adults were gone, they would find a truth.
Like many unseen and powerful demons, "He Who Walks Behind the Rows" could be another name for Satan or it could be a completely separate entity - other antagonists in Stephen King's work also had rather abstract forms, the true form of Pennywise, for example, was said to be an almost Lovecraftian super-entity. "He Who Walks Behind the Rows" is demonic version of the Old Testament God and his appearance is shown in strange mosaic of a pagan Jesus stuffed with corn husks and leaves. In the SyFy version of the movie, He is called the "God of the Old Testament".
There is a popular but as of yet unproven Fan Theory that He Who Walks behind the Rows could also be one of the aliases of Fan favorite Stephen King character Randall Flagg.