The Jack-o-Lantern
The jack-o-lantern predates the pumpkin. Before pumpkins, people in Ireland and Scotland carved turnips, potatoes, and beets, hollowed them out, placed a candle inside, and set them on windowsills. The name comes from a folktale about a man named Stingy Jack, a trickster who outwitted the devil and was condemned to wander the earth forever, his only light a glowing ember inside a carved-out turnip. When Irish immigrants came to America and found the native pumpkin, bigger and softer and easier to carve, the jack-o-lantern became what we know today.
The jack-o-lantern represents the line between this world and the next, kept at bay by a light in a face. The pumpkin is a guardian. That's why it sits at the door.