"He Who Walks Behind the Rows" is the name of the unseen presence that arguably acted as the true main antagonist of the Children of the Corn series - a demonic fertility-spirit of some description, it created a cult of corrupted youths and commanded them into killing their elders so as to start a twisted harvest in which the old would be replaced by the new.
"He Who Walks Behind the Rows" is never seen in the series but its influence was felt throughout, it utilised a number of child-preachers to do its bidding: amongst them was Isaac. The demon's purpose is to create a community which would worship him as a God and follow his will, likely hoping to extend his cult over the entire country, if not the world. To that end, he took control of several gangs of children over the years, through a child-preacher under his compete control serving as his spokesperson and his "High Priest," and had them slaughter all the adults to take over their town. He first manifested in the fictional town of Gatlin in the United States and only remained here or in the nearby agglomerations. At some point, he even searched to produce an heir, by possessing one of his followers and having him impregnate a woman.
"He Who Walks Behind the Rows" has his followers worship him as a twisted parody of Jesus Christ
through ugly crucifixes made of corn crops. No one really knows where he comes from or when he appears, and he can be defined as an evil force rather than a corporeal entity. He seems linked to the cornfield near the town of which he took control, and in several movies he is destroyed (or at least severely weakened) when the protagonists manage to destroy the cornfield or the silo in which he manifests itself. He also seems to need his followers to offer him human sacrifices on a regular basis to sustain himself, somehow explaining why he has all his followers above nineteen years old and all the people who travel through Gatlin sacrificed to the cornfield.
"He Who Walks Behind the Rows" only manifests itself at the end of the original novel and its movie adaptations. He is not described in the book but he proves able to interact with the physical beings when he devours his sacrifices or when he kills the primary protagonist who is fleeing Gatlin through the cornfield. At the end of the first movie, he manifests himself as a gigantic, reddish pink cloud who gradually covers the sky and causes a violent storm while at the end of the third film, he revealingly appears as a giant demonic bloodthirsty monster. His presence is also felt in the very cornfield where the crops are animated under his impulse and in which something menacing progresses towards the protagonists and the redeemed child underground. The demon's evil influence is enough to corrupt almost anyone in a matter of seconds, as demonstrated in one of the sequels, in which one of the protagonists quickly joins the cult and ends up sacrificing himself in his honour. In this sequel, "He Who Walks Behind the Rows" manifests himself inside a fiery silo in which all the sacrifices are thrown.