Kavaxas is a tall and slender red-scaled dragon-like humanoid with large leathery bat-like wings, a spiked tail, four long fingers, two-toed feet (which resemble Jika-tabi boots) and yellow reptilian eyes that bear slitted black pupils.
Kavaxas belongs to a race known as the Demodragons, a kind of demon that has been evoked by evil wizards in the past to bring about disaster to the world. Kavaxas is described as the most powerful of his kind and their current lord.
In the 21st century, after the Shredder had fallen by the hand of the Turtles, his faithful followers, alongside Tiger Claw, discovered a group of creatures whom were faithful to the cause of the Shredder, and formed with them a demonic cult in order to summon Kavaxas to the Earth. Tiger Claw's goal was to use Kavaxas' powers to bring his master back to life. Using an ancient scroll, the Scroll of the Demodragon, and the Seal of the Ancients, Tiger Claw summoned Kavaxas who was angry at a mortal summoning him. Upon being attacked by him in outrage, Tiger Claw shielded himself with the seal; seeing Tiger Claw's possession of the amulet, he complimented him for being "wiser than [he] thought", and reluctantly complied with his orders.
However, Kavaxas secretly pursued his own agenda in which his existence on the Earth benefited him greatly. Namely, he had intended to open up a connection between the Earth and the Netherworld and thereby take dominion over the human world.
To that end, he cooperated with Tiger Claw, whom had brought him the Kuro Kabuto and the heart of the Shredder, both of which were needed for his resurrection of the Shredder. In addition to Shredder, he also revived Rahzar (whom had been killed in a confrontation with the Turtles by Leatherhead) but as undead beings, thereby making them slaves to his will. With his control over Shredder, Kavaxas managed to trick Tiger Claw and succeed in breaking the mystic seal, thus ensuring that he could tear open a gate to the underworld without hindrance and purging the Earth into destruction. However, the Turtles, April O'Neil, Casey Jones, Karai, Splinter’s Ghost, and Leatherhead interfered in his plan and with a portion of gum, Michelangelo succeeded in repairing the seal, thus reversing the invasion, and once again, banishing Kavaxas into the Netherworld with Shredder and Rahzar going with him.
Following Kavaxas’ defeat, the Turtles destroy the seal and spread its remains towards the ocean in order to make sure that he doesn’t return.
As a demon spawned from the Netherworld, and lord of the Demodragons, Kavaxas is a being of pure evil: craving only destruction and chaos where he goes. He sees himself as one who is above mortals and constantly mocks them on their weaknesses.
He does not like to be ordered around very much, as he often shows great disdain whenever Tiger Claw commands him via the aid of the ancient amulet that controls him.
- Demodragon Physiology: As a demodragon from the Netherworld. He also possesses powers far beyond the limits of their reality.
- Super Strength: Despite his rather slender frame, Kavaxas possesses immense physical strength to smack aside and harm the Turtles, April, and Casey with almost no effort.
- Nigh-Invulnerability: As shown in his debut episode, Kavaxas is immune to damage from mortal weaponry. This is best shown when Leonardo's swords shattered like glass as their blades clashed against his face (to which he simply smiled).
- Flight: Kavaxas can use his wings in order to take flight at incredible speeds.
- Pyrokinesis: Befitting his nature as a demonic dragon, Kavaxas is able to breath devastatingly powerful streams of green flames and generate balls of flames from his hands. Additionally, when Mikey snared his arm with one of his nunchucks, Kavaxas simply smiled and sent green flames along the chain into Mikey's arm (which caused him intense pain).
- Laser Blasts: As a (possible) sub-version of his pyrokinesis, Kavaxas is able to shoot green lasers from his fingertips.
- Psychic and Telekinetic Immunity: When April's mental abilities failed against Kavaxas, he explains that it is due to the fact that he is not of their reality.
- Soul Absorption: As shown in The Forgotten Swordsman, Kavaxas possesses the ability to steal a person's soul by touching them with one of his hands. This power is his most deadly, as it leaves his victims dead when their soul is gone.
- Power Absorption: Kavaxas claimed that if he devours someone whole, he would gain that person's powers, as he had planned to do with April.
- Resurrection: The main reason Tiger Claw summoned Kavaxas: he can bring the dead back to life, like he did with Razhar. However in the case of the Super Shredder, Kavaxas can only bring someone back to life if their corpse is complete, in the case of Super Shredder, his helmet and heart were missing, thus, the ritual wouldn't work until they were united with the rest of the corpse.
- Connection to the Seal of the Ancients: Kavaxas has to obey whoever holds a mystical amulet known as the "Seal of the Ancients". While he is bound to this relic, he begrudgingly does as he is told. This amulet also protects the holder from his flames (as demonstrated by both Mikey and Tiger Claw).
- Smokescreens: As demonstrated by Mikey in Scroll of the Demodragon, Kavaxas can very briefly be blindsided by a smokescreen that would give his enemies time to escape.
- Spectro Blasters: Being specially made to take down beings from another reality, the Spectro Blasters damage him, but they don't leave any permanent injuries to him.
- The illustration of Kavaxas in the research texts resembles the 1992 action figure of Hothead, complete with his weapons and helmet.
- Brandon Auman originally created Kavaxas when playing the TMNT RPG.
- The appearance of Kavaxas' laser blasts somewhat resemble the blade of lightsabers, this possibly a reference to Luke Skywalker, a character from Star Wars, whom Mark Hamill (the voice actor of Kavaxas) is well-known for.
- Kavaxas also bears a minor resemblance (primarily in eye and scale color, as well as in personality) to Malefor a villainous dragon (whom Hamill also voiced) in The Legend of Spyro: Dawn of the Dragon.