Legend has it that a man named Jack was so stingy that he couldn't go to heaven after death, and because he made fun of the devil, he couldn't go to hell, so he had to wander around with lanterns until the day of judgment. In order to scare away these wandering souls on Halloween, people carve terrible faces with turnips, beets or potatoes to represent Jack holding lanterns, which is the origin of pumpkin lanterns.
Jack-o'-lanterns are a symbol to celebrate Halloween. Irish people made lanterns out of potatoes or kohlrabi. In the1840s, they came to America with new immigrants. They found a better material than white radish, that is pumpkin, so jack-o'-lanterns became popular.