In his first appearance, he was the only one who submitted an essay to win a chance to spend the day with Grim. Fred was called for Underworld jury duty in the case of the keeper of the Grim Reaper. The case was to decide which of the Grim Reaper's current owners would keep him once Billy, one of the owners, moved. Fred caused much chaos, angering everyone and disrupting the trial, constantly annoying a blue juror and the judge. Despite this, it was his word, "yes" that convinced the Judge to put Billy's family under house arrest. It is unknown what happened after the case, but he went to the blue juror's home to brush his teeth and sleep, only to be angrily reminded by the blue juror that he was in the wrong house.
Fred Fredburger is some sort of elephant demon. He's tubby, green, and has rather small horns. Fred used to have large tusks when he was younger, but these were sawed off by Mr. Bun Bun. In Underfist, Fred is shorter, and less fat. He also began wearing the Underfist uniform tailored by Jeff the Spider.
Fred Fredburger has a very childish and innocent personality and is full of childlike wonderment. He struggles to spell words as evident when he tries to spell his name and gets stuck on the G and R in Fredburger. Despite his childlike personality he is in fact old enough to be called to jury duty and his friend Jeff the Spider claims to be nearly 38. Fred has a strong liking for nachos and frozen yogurt, and things his mama makes him. Apparently his mother told him that babies grow on baby trees, showing that he is quite naive. He is quite easily amused and enjoys spelling his name and saying the word 'Yes'. He also loves TV shows about monkeys that go to camp, imaginary friends and he also loves imaginary monkeys. (Most likely referenceing Camp Lazlo and Foster's Home for Imaginary Friends, two other Cartoon Network shows.)
Fred Fredburger is shown to have a 'Mama', but it is unknown if he has any other relatives. His mama can be assumed to be rather fond of him as she sometimes makes him peanut butter bars or cookies. Fred seems to respect his mama because he mentions her a lot; either referring to the fact that his mama told him something ('It's the best essay ever, my mama told me so.') or has done something for him ('...sometimes she bakes me peanut butter bars...').