I like the imagine the first person who accidentally created it must have been mesmerized, and upon tasting it, would have realize that he had stumbled onto something truly great. He couldn't wait to share it with his village, or tribe.
Popcorn was domesticated in middle America (possibly Mexico) over 5000 years ago. Popcorn likely arrived in the American Southwest over 2500 years ago.
It may have appeared at harvest festivals as early as mid-1600s. The story of popcorn at the Pilgrims' Thanksgiving looks unlikely. Popcorn gained popularity the eastern United States about 1820-1840. Cookbooks mentioned it and there are accounts of eating popcorn for breakfast. But the rise to common use came after several inventors made poppers. A big boost came from movie theaters during the Great Depression of 1930s.
References:
http://www.history.com/news/hungry-history/a-history-of-popcorn