At first, the warm-hearted tale was quite a bit darker; it was supposed to be about a terrifying night of alien visitation to a small farm in Kelly, Kentucky.
Spielberg had other ideas; he was able to talk writer Melissa Mathison into lightening up the script and creating the E.T. character. At that time, Mathison was girlfriend to Harrison Ford.
Obviously, the right script was used. The case that the original script was based on was the The Kelly Kentucky Aliens.