Like all ghosts, he is transparent, with her bones visible inside his body. He has a glowing skull. He wears a referee whistle around his neck, and a headband around his skull.
It's unknown when this ghost was alive or how he died. He now oversees wrestling matches held between ghosts.
After Engilbjort challenges Hilda, David and Frida to a wrestling match for the book she supposedly stole, the referee appeared from his grave to oversee the match. When Engilbjort used her ghost powers to escape the three kids, the Referee called her out on this and warned her not to cheat again. Despite this, he didn't stop her when she cheated a second time and thus won the match. Hilda called the Referee out on this, but he ignored her.