The titular character. He's a kind-hearted rat-like creature who rules over Ratboy's Kingdom.
- Catchphrase: "Knock knock", which he usually says when greeting people.
- Primary-Color Champion: As the main character, it's fitting that he has yellow "fur", a blue cap and shorts, and a reddish-orange T-shirt.
- Protagonist Title: The series is named after him.
- Rubber Man: It's later shown that he has the same stretchy abilities as Little King John.
- Synthetic Voice Actor: His high-pitched voice is clearly computer-generated.
- You Dirty Rat!: Averted. Despite being a "Ratboy", he is friendly and caring.
Ratboy's eternally optimistic friend.
Another friend of Ratboy's.
Summer Solstice Baby
- Love Triangle: Between her, Ratboy Genius and Little King John. The series "Ratboy Dreams Minecraft" revolves around the latter's kidnapping of Baby and the former's rescue.
Little King John
A minor antagonist in the series, who seems to be on the way to making a HeelFace Turn
- Breakout Character: He was popular enough to spawn his own series called "The Flood", which later on, is revealed to be a Shared Universe with "Starship Genius".
- Big Bad: In "Dreams Minecraft"
- Body Horror: Mostly Played for Laughs, but he can stretch his body in the most unnerving way possible.
- Cool Crown: He wears a golden crown.
- HeelFace Turn: The Series Finale for "The Flood" cements this entirely. To put it, he started out as the Big Bad of "Dreams Minecraft", then the Villain Protagonist for the first few episodes of "The Flood", then a Nominal Hero in later episodes, and now a flat out Hero by the end.
- Jerkass: Mainly in "Dreams Minecraft", but he still has his moments in The Flood.
- Pride Before a Fall: Much as he started off as an villainous king, The Flood is all about LKJ losing everything he had, surviving the apocalypse, and learning to value other people, which results in a Jerk-to-Nice-Guy Plot.
- Psychopathic Manchild: Although he leans more strongly towards "manchild", he has shades of this, such as when he steals Happyman's factory. "This is mine! This is mine! This is mine, too!"
- Rubber Man: He can stretch his neck and limbs to rather disturbing lengths.
- Synthetic Voice Actor: Like Ratboy, his voice is computer-generated.
- Trademark Favorite Food: Potato knishes, to the point that about half of his Villain Song is about how much he loves them.
- Wicked Cultured: He can play the piano and the pipe organ, and one video even features him playing a fugue that he composed himself.
- You Dirty Rat!: The only ratboy who is actually evil.
- Beneaththe Earth: In Happyman Opera, Fred says that Sue lives "in the underworld," a description which appears to be more literal than biblical.
- Informed Attractiveness: Bob comments on Sue's beauty when he meets her, even though she's drawn with Dorin's signature crudeness.
- Losing Your Head: Her head can fall off.
Old Man Fingerhead
A doglike character met by Little King John after he escapes his sunken kingdom, who agrees to tag along on his journey to find a new land.