Jeff has a large corncob (with the kernels) for a body, it having limbs sprouting out of it. He wears the leaf of the cob like a shirt, and does not have a neck. He also wears a pair of brown shoes and a belt.
Jeff has been shown to be generous, as seen in "The Gripes," when he donates money to a "poor" Gumball and Darwin. But when he (and others) hear about Gumball and Darwin lying to them about this, he joins an angry mob against them.
In later episodes, he displays an awkward personality, often making mistakes and embarrassing himself, such as during "He's Back" in "The Founder" during which he mispronounces "wiseness," sings part of the chorus too late, and gets stuck in the elevator.
- "The Castle": He is at the party at the Wattersons' house.
- "The Internet": He is one of the drivers involved in a massive pile-up.
- "The Kids": He gets fired.
- "The Extras": His first major role. He is seen with the citizens singing "Just Notice Us."
- "The Gripes": He appears in the mob of citizens donating to the Wattersons.
- "The Law": He appears in the crowd watching the Donut Cop arrest Felicity.
- "The Shell": He is in the theater audience watching the play.
- "The Butterfly": He can be seen in the Elmore Wings plane.
- "The Oracle": He is one of the many people who want to be the 1,000,000th customer.
- "The Safety": He is part of Darwin's new police force.
- "The Spoiler": He is at the cinema.
- "The Return": He is in the audience watching a movie.
- "The Others": He can be seen in the crowd of citizens on the highway.
- "The Check": He is seen working at Darwin's business.
- "The Sale": His second major role. He and his wife are planning to buy the Robinsons' house, but are scared away by Gumball, Darwin, and Richard.
- "The Parking": He is part of the car pileup.
- "The Romantic": He dances as part of the musical number for Gumball's first clue.
- "The Apprentice": He is seen in the supermarket running away from Gumball and Patrick in a golf cart.
- "The Wicked": He is attacked by squirrels.
- "The Traitor": He is at the cinema again.
- "The Nest": He runs away from the Evil Turtle's babies.
- "The Bus": He is seen in his car.
- "The Misunderstandings": He is seen at the mall hosting an auction.
- "The Blame": He is at the PTA meeting.
- "The Fury": He is in his car stuck in a traffic jam.
- "The Scam": He is seen chanting to Gumball and Darwin to hunt Gargaroth.
- "The Disaster": He is seen at the mall.
- "The Rerun": He is seen in the mall.
- "The Boredom": He is at the mall.
- "The Choices": He was in the crowd at Nicole's graduation and when she became the president in her flashback.
- "The Code": He is seen in the bus.
- "The Ollie": He laughs at Gumball.
- "The Cycle": He attends prom night in Richard's flashback.
- "The Diet": His water bottle is stolen by Richard.
- "The Sorcerer": He is swallowed by the troll.
- "The Menu": He is seen in the mall.
- "The Worst": He is seen in a photo as an "Employee of the Month" of the Rainbow Factory.
- "The Nuisance": He is seen in the crowd.
- "The Line": He is one of the people running to the first showing of Stellar Odyssey.
- "The List": He is seen cheering for Gumball and Darwin during a marathon.
- "The Sucker": He is seen inside an airplane.
- "The Vegging": He becomes a mutant and attacks the scientists.
- "The Father" He drives a car.
- "The Cage": He is seen in the crowd cheering for Mr. Corneille.
- "The Anybody": He is at the Elmore Cinema.
- "The Faith": He is seen spectating a football match, then warns Gumball and Darwin about the hole in the ozone layer.
- "The Shippening": He is at the mall.
- "The Brain": Anais dreams that he drives his car.
- "The Founder": He works at Chanax.
- "The Schooling": He is in the cinema.
- "The Intelligence": He gives Gumball and Darwin a vacuum nozzle.
- "The Potion": He is looked at by Hector .
- "The Spinoffs": He is outside of Joyful Burger.
- "The Awareness": He cheers for the melted cheese guy.
- "The Slip": He pushes Richard out of a plane.
- "The Possession": He is in the background.
- "The Wish": He drives a car.
- "The Factory": He works at the Rainbow Factory.
- "The Agent": He drives his car.
- "The Web": He works at the Rainbow Factory.
- "The Mess": He is saved by Gumball.
- "The Revolt": He is attacked by the objects.
- "The Decisions": He is at the mall.
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- His first name is revealed in "The Check," and his last name was revealed in "The Sale."