Parker Jamiroquai Cloud

Voiced by: Becky Robinson

• Ambiguous Gender: Per the creator, Parker has no true gender, as of course clouds do not have genders. That said, Trabbic has actively avoided using labels such as “agender” or “non-binary” to refer to the character, his stated philosophy being that "the neat thing about a cloud is that different viewers will see different things", and that he hopes anyone watching relates to Parker regardless of their gender. Pre-release materials largely used masculine pronouns to refer to the character, whilst Parker's voice actor, Becky Robinson, is female.
• Animate Inanimate Object: Needless to say, real-life clouds are nowhere near as peppy as Parker.
• Beware the Nice Ones: He is a pretty nice guy but being a cloud, he can turn into a giant storm cloud when provoked enough.
• Blush Sticker: Parker has permanent ones on their cheeks.
• Cheerful Child: Parker is always happy and excited.
• Color Failure: Parker, who is usually clad in a colorful rainbow unitard, becomes quite literally dull and gray when they're depressed.
• The Cutie: Parker is so adorable, happy, and naïve.
• Dark and Troubled Past: Parker's backstory is that they're a “reformed raincloud” who used to “rain on people's parades, but now wants to brighten everybody's days”. They don't seem to let that get them down, though.
• Kids Hate Chores: Parker is initially thrilled to help out with the chores around the ship in "Chore or Less", but although he has a lot of fun with them, they rush through the entire list at once and does a messy, mediocre job; when Angus walks them through the proper (incredibly boring) way to do everything, they quickly loses their enthusiasm for it. Eventually, they learns that chores are a constant thing that nobody entirely enjoys doing, but the important thing is to try your best at it.
• Kids Prefer Boxes: The short "Unboxing" concerns Parker receiving a package, but he prefers to not unbox it immediately and have some fun with the box first, despite Angus' protests. Among many other things, they take it to the cinema, showers with it, and pushes it on a swing. When they eventually do open it, they finds out that there's ice cream on the inside that has since gone bad. Parker decides to eat the ice cream, and as a result gets no ill effects considering he's not an organism.
• Keet: Is very enthusiastic and energetic.
• Me's a Crowd: Parker can apparently create mini-versions of themselves. They created a crowd of Parkers to cheer them on at baseball in "BURT! The Musical".
• Named After Somebody Famous: Parker's middle name is "Jamiroquai".
• Ocular Gushers: Parker's tears are shown to flood the entire Post. It's implied that it's because they are a cloud, and thus they "rain" instead of crying.
• Species Surname: Parker's last name is Cloud.
• Voluntary Shapeshifting: Parker can do this of course, considering he's a cloud. Makes sense as well, as clouds don't have much of a consistent shape.
• You Wouldn't Like Me When I'm Angry!: Being a raincloud, Parker unleashes a nasty storm anytime they get tipped over the edge.

Angus Roy Shackleton III

Voiced by: John DiMaggio

• Butt-Monkey: When the Middlemost Post go on misadventures, he's the one who's most likely to get the short end of the stick (e.g. "Parker Saves Christmas").
• Nice Guy: Don't let the gruff sailor exterior fool you. He's one of the kindest and most thoughtful fellas on the mountain.
• Screams Like a Little Girl: He is prone to screaming exactly like this.
• Strong Family Resemblance: To his father, Angus Shackleton Junior.
• Token Human: He's pretty much the only human in Mount Middlemost.
• Top-Heavy Guy: A ridiculously wide torso atop a pair of toothpick legs.

Russell is a magic walrus whose stomach is so vast and huge that it doubles as a storage room for the Middlemost Post Office.

• All Animals Are Dogs: Russell is a walrus, but behaves more like how a pet dog would.
• Crossdresser: She proudly wears a suit on her date with Winifred, which later gets turned into a vest.
• Gender-Blender Name: Despite the male name, Russell is a girl.
• Hates Baths: She freaks out whenever the word bath is mentioned out loud.
• Intelligible Unintelligible: Russell only makes grunts and dolphin sounds, but Parker and Angus can understand her.
• Interspecies Romance: With Winifred the narwhal.
• Queer Establishing Moment: Is revealed in "To Narwhal, with Love" to be a lesbian when she falls in love with Winifred, a female narwhal.
• The Smurfette Principle: the only girl in the main cast.
• Stomach of Holding: Russell can store all sorts of objects inside her belly.
• Team Pet: The animal representative of the Middlemost Post. She cannot speak, but that doesn't prevent her from joining in the fun.
• Tertiary Sexual Characteristics: She's purple and has long eyelashes to indicate her gender.
• Warm-Hearted Walrus: She's a friendly little walrus.

Voiced by: Kiren

• Gadgeteer Genius: Builds several impressive mechanical devices, including a Mini-Mecha she built for herself.
• Ridiculously Cute Critter: Is an adorable worm like creature.
• The Stoic: Usually speaks in a deadpan voice.

Mayor Steven Charles "Steve" Peeve

Voiced by: Colton Dunn

• Evil Is Petty: Downplayed. He's not evil, but he is antagonistic. He hates Middlemost Post because the ship is in the way of his sunlight.
• Mayor Pain: While not particularly evil in general, he will often let his grudge against Angus and the Middlemost Post (held because Angus’s ship, parked atop Mount Middlemost, leaves City Hall in its perpetual shadow) get in the way of his mayor duties to the detriment of his citizens; for example, purchasing a robot to drive the post out of business while not accounting for the damage it causes.
• Unknown Rival: To Angus.

Voiced by: Johnny Pemberton

Ms. Pamela "Pam" Ingrid McLaurin

Voiced by: Kamali Minter

• Family Business: Ms. Pam gave up her Hollywood dreams to work in the family toast business.
• Cordon Bleugh Chef: Ms. Pam will serve anything as long as it's atop a piece of toast.