The Pumpkin King's real name is Francis and is in charge of a pumpkin patch in Wuzzleburg Forest where the largest pumpkins grow. His noble steed is Candy Corn, the fire-sneezing horse.
The Pumpkin King has a pumpkin for a head with leaves around his neck, and wears a crown. He also wears a purple shirt, belt, yellow gloves, green pants, and what appear to be elf shoes.
The Pumpkin King is featured in the episode March of the Pumpkins. Walden reads from a book that the Pumpkin King gets very angry when people take his pumpkins and that his noble steed, Candy Corn, breathes fire. Widget adds that you know he's coming when you hear him say "Boogity boogity!"
However, when Wubbzy meets the Pumpkin King, he isn't mean or angry at all. He explains that he loves it when people take his pumpkins and offers Wubbzy to take as many as he wants. He summons his noble steed, Candy Corn, and clarifies that she doesn't breathe fire; but then Candy Corn sneezes and fire comes out, so the Pumpkin King adds, "...except when she sneezes." When Wubbzy and Daizy first hear the Pumpkin King say "boogity boogity", they run and hide; then, when the Pumpkin King asks why they're hiding and they say because his "boogity boogity" meant he was mad, the Pumpkin King clarifies that "boogity boogity" just means "hello" in pumpkin talk. He loves when people takes his pumpkins , and his horse only breaths fire when be sneezes.
Obviously, those who wrote Walden's book had never met the Pumpkin King himself!