General Reginald Peter Skarr is Billy's neighbor, and a retired villain.
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 to an entertainment company, who didn't want anyone else to take over the world (a jab at Cartoon Network for cancelling the show). Afterwards, he retired and moved to Endsville, where his house happened to be next door to Billy and his family.
He has a blind left eye with a jagged scar under it. He wore a blue suit and oddly shaped hat when working for Hector.
He is bald (which is sometimes used as a gag) and has a large, downward pointed nose.
In Underfist, he has a large grey moustache and goatee, and wears a bright blue uniform that includes a beret.
When he worked for Hector Con Carne, he sometimes tried to overthrow Hector and take over his organization to take over the world himself.
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 afraid 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.
- In the episode "Emotional Skarr", when he fantasizes about ruling the world himself, his symbol is his scar in a circle similar to how the swastika was positioned. He also was shown in the same fantasy having an eagle on his hat, positioned in the same way as the Nazi eagle symbol. However, this is only evident in one scene.
- According to the show's intro, he got his scar from running with scissors.
- Coincidentally, this is also how Hoss Delgado lost his own eye (as well as his arm and leg).
- General Skarr is an homage to Herr Starr from the Preacher series.
- Skarr's first name was revealed in the intro of Evil Con Carne, and first mentioned in Billy and Mandy's Big Boogey Adventure.
- He has appeared as an official character in more TV series than the characters from all the other shows combined.
- Skarr's plant form heavily resembles a Pikmin from the video game series Pikmin.