Long ago in The Hidden Kingdom, animals and humans lived together in peace... until the evil HighRoller convinced the animals that humans were their enemies. HighRoller and his animal armies mistreat humans and drive them from their homes. But there is hope, thanks to a rebel force of young heroes. This team of heroes live in a giant abandoned turtle shell called “Big Green” and fight HighRoller to protect the humans and restore peace in the Hidden Kingdom.
- Commander ApeTrully (voiced by Ian James Corlett) - Commander ApeTrully is the eccentric, well-meaning leader of Big Green. Commander ApeTrully formed Big Green in hopes of restoring friendship between animals and humans. In most episodes, Commander ApeTrully would end up captured by the animals he visits when trying to make peace with them with piles of gold. When in danger, he activates the device on his head to call for First Squad. In "Parrot Castle", he is revealed to be the king of the Monkeys (Monkey King) in disguise as he was the first to see through HighRoller's lies but keeps it a secret to preserve Big Green's morale (in his words, he does not want humans to know it was a monkey who led them). In "Shark Castle" and "Crab Castle", he would accompany First Squad to the underwater castles when riding in Sammo the Whale in order to make peace with the aquatic animals that way. His name is a joke referring to the fact that he's an ape, truly. In the Chinese dub, he was named Song Chang and there was no explanation saying he was a monkey. Classified on the official website as Hero 001. The only thing he can do is use his monkey skills and use almost an endless supply of gold seen in every episode. In "The Rise of Lin Chung", it is shown that Commander ApeTrully owns a diamond that is larger than his body.
- Woo the Wise (voiced by Adrian Petriw) - Woo the Wise is a human inventor who was the first person to be convinced to join Big Green. At some points, his robe tends to rise up. He wears a fake mustache to make himself look older. A running gag is that he says that he knows what he is doing, yet he really has no idea what to do in his head, thinking "My head is as empty as a balloon!". In a flashback that was seen in "Folk Game Competition II", he was a former classmate of HighRoller. In "Pitched Battle of the Air Force", Woo the Wise invented a special crystal that could assemble animals into one creature, which he did when he tested on four animals allied with Big Green (Elephant King, Peacock Queen, Octopus King, and Scorpion King) and later merged two hens, Snake King, Crocodile King, and Deer King into a Chimeric Dragon to fight High Roller's fake Black Dragon. In "The Bronze Giant", Woo the Wise makes up the blueprints for upgrading Big Green base into a mobile battle station and works on it with the other members of Big Green. Classified on the official website as Hero 003.
The Big Green's elite warriors. Among its members are:
- Mr. No Hands (voiced by Ian James Corlett) - Mr. No Hands is the military leader of Big Green's First Squad. The tassel of his hat spins like a helicopter allowing him to fly. He keeps himself in a stockade because he can’t stop tickling himself, hence the name.
- Lin Chung (voiced by Andrew Francis) - Lin Chung is known by some as the most accomplished, most skilled warrior in all of Big Green. He possesses the legendary Panther Vision, which allows him to see great distances, or to see the world in slow motion while he moves with terrific speed. He is also somewhat obsessed with drawing, and he can't take criticism. It is known that he will drop a whole battle just to paint a picture.
- Jumpy Ghostface (voiced by Brian Drummond) - Jumpy Ghostface is the king of the rabbits. He is a talented, straight-ahead fighter who dives headfirst into dangerous battles without flinching an ear. He joined Big Green after being defeated in a jump rope battle. His weapon of choice is a jump rope. He also uses carrots as weapons, either throwing them like shurikens or biting off the top and tossing them like grenades. He also has a habit of daydreaming, even in the heat of battle. He can "speak human" but only in short phrases.
- Mystique Sonia (voiced by Kelly Sheridan) - Mystique Sonia is a tough seasoned warrior, but also a stereotypical girl. Her attack involves spinning her tongue around to perform gusts of wind. Since she is cursed with a spell, anyone who tells her they love her three times in a row turns into a Yaksha.
- Yaksha - Yaksha is a purple, non-speaking creature that rests upon Mystique Sonia's head. The nature of these creatures remains mostly unknown. It is also extremely flexible, being shown to turn into a ball, a purse, a fan, and even extend it's arms.
- Mighty Ray (voiced by Ian James Corlett) - Mighty Ray is definitely the burly force of First Squad. He has the power to shoot bolts of powerful energy from his eyeballs. To re-charge his eyeballs, Mighty Ray must eat bananas which make him gag. His eyeballs are also removable.
The Big Green's secondary warriors. Among its members are:
- Alpha Girl (voiced by Tabitha St. Germain) - The leader of Big Green's Second Squad who serves as a rival to Mr. No-Hands.
- Golden Eye Husky - A liger that is a member of Big Green's Second Squad.
- Kowloon - A human member of Big Green's Second Squad.
- Hurricane Lee - A warrior of Big Green's Second Squad and brother of Archer Lee.
- Archer Lee - The archery member of Big Green's Second Squad and brother of Hurricane Lee.
- Twin Masters (voiced by Scott McNeil) - Twin Masters is a two-toned demon who is HighRoller's master and uses him in his overall scheme to plunge the world into chaos. Twin Masters' head resembles a skull with small, glowing yellow pupils. On his right side, he is red and somewhat jagged, resembling lava and fire. On his left side, he is blue and wavy, resembling water and ice. His red half speaks with a gruff voice, while his blue half speaks with a more shrill voice. Twin Masters was once a human warrior prince named Yang Tu (voiced by Brad Swaile) who wanted to take over the Hidden Kingdom. Lin Chung tried to change Yang Tu's fate, but Yang Tu fell into a deep volcanic pit into the Earth. Yang Tu was trapped inside until he became Twin Masters and mastered the power of chaos. Among Twin Masters's powers is the manipulation of unstable chaos energy, making his attacks utterly destructive. A few of the animals know of him from legends, rarely appearing outside his cave until the actions of First Squad force him to reveal himself and take a more active role. In "The Return of the Pterodactyls", he commanded the bald eagles to drink the sap from the ancient trees of the Hidden Kingdom which turned them into pterodactyls. He also turned animals into monsters through schemes involving a storm while having Mighty Ray's eyeballs and later enchanting the Owl Amulet. He hypnotized Second Squad which means he has hypnosis powers. By the end of Season 2, Twin Masters gains water from the lake of Tai Chi and encases himself in a giant cocoon to assume a powerful form. His skull-like head becomes more luminescent red and blue. He also has a snake tail in place of legs, with spikes at the end of his tail. It took the combined abilities of Big Green and all the Animal Kings and Queens to form the Bronze Giant in order to destroy Twin Masters.
- HighRoller (voiced by Brian Drummond) - The primary antagonist of the series. As the new Emperor of the East Citadel, HighRoller gets to do whatever he wants and what he typically wants to do is attack humans (or get animals to attack humans for him), eat candy and play games.
- Zebra Brothers (voiced by Adrian Petriw and Brian Drummond) - Two zebra twins that serve HighRoller. Sparky B is a black and white zebra and Sparky W is a white and black zebra. They tend to argue a lot and often end up fighting in the middle, and the end of a battle.
- Bearstomp - Bearstomp is the armored King of the Bears who wears a helmet with a cannon on it. He acts as HighRoller's bodyguard. He is often shown blowing nose bubbles while asleep. One of his arms has been replaced with a retractable winch/pincher (suggesting that he may have been injured in battle). It is unknown as to how he acquired such a device, but it seems likely that HighRoller gave it to him as an incentive to enslave humans and become a prominent leader of HighRoller's army. In "Firework Festival at East Citadel" and "Strongest Punch & Kick", Bearstomp is shown to have the ability to combine with High Roller to form the "High-Stomp" formation which allows High Roller to be much tougher. In "Gladiators" Bearstomp is among those who were captured by the Minotaur's minions. First Squad and Bearstomp had to work together to escape the Minotaur. When Lin Chung offered Bearstomp to switch to their side, Bearstomp just hits Mighty Ray and returns to East Citadel. Although Lin Chung stated that Bearstomp is their enemy, he was their ally in the battle against the Minotaur. In "The Bronze Giant," Bearstomp joins Big Green to help form the Bronze Giant (classified as Hero 052). Once Twin Masters is destroyed by Bronze Giant, Bearstomp and the Zebra Brothers leave with HighRoller to return to East Citadel.