Reginald Skarr, better known as Principal Skarr, was Billy's neighbor, and a retired villain. He has a prosthetic glass eye by unknown circumstances. He used to work for Hector Con Carne (from the show Evil Con Carne, which was paired with The Grim Adventures of Billy and Mandy originally as Grim & Evil), but left after Hector was forced to sell their island headquarters and their army (as it turns out, Mandy bought the island and a television company bought their army). Afterwards, he retired, and ended up living in Endsville, next door to Billy. He has many weapons and his old military uniform in his home as a memento of his time working for Hector Con Carne. He is often tempted to return to his evil ways, but he tries to stop himself from becoming a villain again by gardening. He hates Billy very much due to the fact that he is annoying and frequently destroys Skarr's garden. He is also terrified of Mandy, and wants Grim's supernatural scythe. He stole Grim's scythe once, but thanks to Pud'n and Mindy, Grim got it back. Before he got his brain returned from the Brain Eating Meteor. He holds a vast amount of hatred towards both Buttercup and Butch more than he had for Billy. He moved to Megaville/Townsville in order to get away from Billy, but to no avail.
The most notable thing about Skarr is that he has been blinded in his left eye, by unknown circumstances. He has many weapons and his old military uniform in his home as a memento of his time working for Hector Con Carne. He now is a principle and thus wears a neat uniform. He used to wear hats because of his baldness but now doesn't anymore.