He is the entity that brings presents to good boys and girls on Halloween night, as popularized on the Peanuts television special "It's The Great Pumpkin, Charlie Brown".

It is believed the legend of the Great Pumpkin originated in 12th century Ireland at a time when the Irish were still carving turnips into Jack-O-Lanterns for their Hallow's Eve festivities. According to legend the young children who carved the turnips were frustrated over the difficulty in carving this small root vegetable. Their wee fingers kept getting nicked by their knife blades when the knives slipped on the smooth surfaces of the turnips. The story goes that one such child, a 7 year old by the name of Phaneus, prayed on the evening of October 30 before he went to sleep, for divine intervention to bring him an easier vegetable to carve.

When he awoke the next morning beside his bed was a strange orange globelike vegetable twice the size of his head. When Pheneus touched it he realized this was the answer to his prayer, and he therefore immediately and gleefully began carving it into a Jack O' Lantern.

Upon carving what we know today as the pumpkin, he showed his creation to the other children of his village, and initially they were so afraid. But then the glory of the higher power shone about them, and said, "Behold, I give you tidings of great joy, for this is the Great Pumpkin; peace on Earth, good will towards men.
"The Great Pumpkin rises from the pumpkin patch every Halloween to give presents to good boys and girls!"
by Peanuts Anonymous July 2, 2008
Basically a ripoff of Santa Claus and the Easter Bunny (a ripoff himself of Santa Claus, and a lame one at that) who apparently is a giant pumpkin that appears in pumpkin patches toward midnight of Hallowe'en. He gives out candy to those who bbbbbbbbeeeeeeeeeellllllllllliiiiiiiiiiiieeeeeeeeeeeevvvvvvvvveeeeeeeeeeee. Popularized by the comic strip and TV show Peanuts by Linus, my man, who invited Lucy to go with him to the patch to see the Great Pumpkin. Twice.
Linus: Yo, luce, ya wanna go see the great pumpkin with me? (not the great popkin)

Lucy: You and me all alone in a pumpkin patch in the dead of night, where anything can happen? SURE!!
by Mr. Wallflower November 2, 2013
Great-Pumpkin: (verb)To be "Great-Pumpkined" is to be let down in a big way, especially when others have been doubting or making fun of your sincerity over what you're hyped up; also, to be stood-up by someone.

An allusion to "It's the Great Pumpkin, Charlie Brown!" where Linus is convinced that the Great Pumpkin will come to his sincere pumpkin patch, and convinces Sally to join him. The Peanuts gang teases them and warns them they are making a big mistake. The Great Pumpkin never shows and Linus, still convinced that the Great Pumpkin will materialize, mournfully yells into the sky: "Oh Great Pumpkin, where ARE you?!"
We really hope this forecasted snowstorm doesn't Great-Pumpkin us; we could really use the snow-day!

That gift wasn't as amazing as I expected; I feel like I was Great-Pumpkined.

Let's go cheer up our boy; heard he got Great-Pumpkined by that girl on that dating site.
by AmericanShamrock March 21, 2018
On Halloween going trick or treating at an elderly person's house
Hey Mark lets go visit the great wrinkled pumpkin
by fitzdogg December 14, 2010