Romeo is an evil young mad scientist who plans on world domination with robots, inventions or anything to make the world love him.
Romeo wears a mad scientist coat, boots, pants, goggles and a lightning bolt-shaped black and white hairdo.
- Romeo is the first and primary villain in the PJ Masks (series).
- Romeo knows about the PJ Masks' secret identities.
- Romeo has been seen twice without his goggles. First in "Owlette and the Flash Flip Trip" on book covers, and again in "Gekko and the Mighty Moon Problem".
- The white streak in his hair could be a reference to Cruella DeVille, a woman from the 101 Dalmatians series who also has black and white hair.
- His hairstyle is quite similar to Ryder from PAW Patrol.
- In "Gekko and the Mayhem at the Museum", he revealed that he likes Double Tofu Pistachio ice cream.
- In "Speak UP, Gekko!", there was a brief animation error that removed his legs.
- Romeo has called the PJ Masks these names:
- PJ Masks: PJ Pests, PJ Monkeys, PJ Stinks, Super Stumblers, PJ Pains, PJ Dodos, Daytime Dodos, PJ Do-Gooders, Non-Speaking Ninnies
- Catboy: PJ Pussycat, Kitty Litter Boy, Kitty Cat, Kooky Cat, Pussycat, Biker Boy
- Owlette: Feather-Brain, Bird-Brain, Birdy
- Gekko: Lizard-Legs, Lizard Boy, Lizardy Loser, Loopy Lizard
- In Romeo Undergear, it is revealed that Doctor Undergear is Romeo's grandfather.
- He keeps a special cog pendant with a picture of him and his grandfather taped on it underneath his mad scientist jacket.
- He has a Shark Ship for a ship, two giant mechanical crabs, and a Robo Bird like the ones at Gear Island as pets.
- Romeo has a crush on Catboy's female alter ego, Catgirl, in Girls Will Be Heroes, and he has a crush on Amaya in Romeo and Owlette, but then was dumped by her after she realized that he was using her against her friends, and he made Juliet the witch his own professional girlfriend in Romeo and Juliet.
- In All Aboard The Steamtrunk, Romeo's favorite Fantasy Forest animal is a Steamtrunk.
- Also in Owlette and the Peppermint Plattys, the Peppermint Platty is also Romeo's favorite Fantasy Forest animal.
- He is shown to be very jealous of Sofia and her inventions, the Magical Creature Power Suits and the Magical Creature Power Discs.