|Series||The Grim Adventures of Billy and Mandy|
|Voiced by||Maxwell Atoms|
Jeffrey "Jeff" the spider is an extremely generous spider who supposedly is the son of Billy, since Billy is the one who hatched him from his egg. Since Billy hates bugs, especially spiders, he repeatedly tries to kill Jeff, despite his kindness. Jeff's best friend is Fred Fredburger and both of them now work, along with Hoss, for a superhero team called "Underfist."
FusionFallIn FusionFall he appeared for the first time in the Birthday Bash event, and his model, like Zon's and Ship's, didn't move. He later appeared at Habitat Homes during the Mother's Day event looking for the Blowfish egg after Billy kicked it, though he is now gone.
Like Zon and Ship, Jeff received animation when added once more after the Birthday Bash.
You can also get a Jeff Helmet, and his eggs as thrown weapons.
- Jeff has appeared only for the Birthday Bash and Mother's Day events. He was removed after both events were concluded.
- In Underfist: Halloween Bash, it is revealed that the movie's main villain, Bun-Bun, is the one who caused Billy's fear of bugs and Jeff.