Rat Man Freak (voiced by Jason Biggs) - A humanoid mutant rat who just appears in "Of Rats and Men." When the Rat King is planning to turn the humans into rat people with his Mutagenic Growth Serum, Aristotle tells him that the serum's not perfected. Then, both the Rat King and Aristotle witnesses the man he tests the serum on mutates into a hideous, disabled monstrosity. His only line was "Cheese! Please give me CHEESE!" His name is not mentioned in the show, but the name comes from the credits.