The Creditor is a loanshark parody of The Predator, who loaned Shake the money to buy a ridiculous stretch Hummer in The Creditor then began hunting him when he couldn't make the payments on the loan.
Like the regular Predator, he enjoys ripping out and collecting people's skulls and spinal columns for fun in addition to his loanshark job. Shake met him at a club in which he killed several people and collected their skulls and spines, and Shake later assisted him in disposing of various bodies from another club in which he (again) randomly killed and dismembered various people.
Eventually, after Shake tries to stand up to him, The Creditor kills and collects the skulls of Frylock, Shake, and Shake's therapist, but is unable to do so to Meatwad (since he has no bones).
After killing Shake, the whole episode is shown to be a bedtime story The Creditor is reading to his 2 children at the end. He only appears in The Creditor.