In his struggle to clean his kitchen and rid the entire cafeteria of "mystic" implements, Baron Draxum trapped an Oozesquito in a pot of blended meat and sauces - ostensibly, "Sloppy joe" mix. The Oozesquito mutated the meat mix, which escaped and began searching for things to eat.
As it ate more and more, Joseph began to progressively grow incredibly large. At the same time, Draxum and April attempted to hide Joseph from Vivian Slopworth and the other lunchpeople who were present to determine Draxum's eligibility for the Lunchperson of the Year award. Their intervention attempts did not last, however, and Joseph burst into the main lunchroom where the lunchpeople had gathered. With quick thinking, Draxum used a pair of ladles to slice up Joseph and spread him across hamburger buns. The threat was defeated, but the chaos caused Draxum to lose his eligibility for the award. Thankfully, the other lunchpeople, knowing what sort of person Vivian is, accepted Draxum as one of their own.
Later, it is revealed that Draxum had kept a small portion of Joseph alive. He begins to feed him, but starts with vegetables so that he does not grow out of control.
Sloppy Joseph can eat anything no matter the size. This causes it to become bigger and bigger.
- When Sloppy Joseph comes out of someone's locker after eating someone's sandwich, he wears a pair of sunglasses that make him look like a sloppy version of Krang's Android Body, including the fish skeleton atop his head, which resembles the fork-like antenna on top of the android body's head.
- In Battle Nexus: New York, when Joseph was in charge of the cafeteria kitchen, he did a slide with a instrumental song of the opening for Bob Seger's Old Time Rock and Roll. This is a reference to the film Risky Business, in which Tom Cruise's character Joel Goodsen does something similar.