Onaga, also known as the Dragon King, is the primary antagonist of Mortal Kombat: Deception. First alluded to in Mortal Kombat: Deadly Alliance, he is a mighty draconic creature and was the former emperor of Outworld. He was killed millennia before the events of the first Mortal Kombat game, but would return to life when his soul, bonded to an infant dragon, would merge with the body of the Saurian known as Reptile.
Millennia ago, Onaga, also known as the Dragon King, was the true ruler of Outworld. Hoping to gain eternal life, he ordered the last known dragon egg to be kept, hoping that the blood of an infant dragon would grant him immortality. However, he died before this could be fulfilled. Shao Kahn, one of his chief advisors, had him poisoned and took over his rule of Outworld. His army, however, was kept in a mummified state. This army was considered invincible because Onaga possessed the innate power to raise the dead. By means of constant resurrection during battles, his army truly was undefeatable. During the millennia that followed, Onaga was apparently forgotten.
Quite some time before Liu Kang's victory over Goro and Shang Tsung at the Shaolin Mortal Kombat tournament, Onaga communicated through death to Shujinko through an avatar named Damashi. He persuaded Shujinko to embark on a quest to unite the Kamidogu, claiming he was carrying out the will of the Elder Gods, as well as granting him the power to learn the fighting techniques of warriors he encountered. Shujinko readily embarked on his quest, beginning to set in motion events that Onaga hoped would lead to his eventual return to power. Additionally, a sect of holy men still dedicated to him had been guarding the egg of the last great dragon in a chamber of molten lava. During the events of Mortal Kombat II, they captured the Outworld elemental Blaze, who was forced to guard the egg until it was ready to hatch and revive the king.
A few years later, Quan Chi and Shang Tsung, the Deadly Alliance, used their powers to resurrect Onaga's army. Their plan was to use this army to conquer Outworld and eventually, all the other realms as well. Raiden embarked on a mission with the Earthrealm warriors to Outworld to stop their plans, but his attempt ultimately failed. His comrades were slain and he himself was defeated by the Deadly Alliance in person. However, their victory was short-lived. The vampiress Nitara convinced Reptile to help her access the chamber of the last dragon egg. The chamber also held an orb that would separate Outworld from the vampire realm. After she destroyed the orb, Nitara left, but Reptile, feeling betrayed, arrived almost as soon as she transported herself to her native realm. At that moment, the egg hatched and sent its energy into Reptile, which fulfilled the prophecy of Onaga's return. The Dragon King, as such, used the transformed body of Reptile as a host, after he had gained the ability to raise himself from the dead through Shujinko's actions.
Just as his army stood ready to receive commands from Quan Chi, who had emerged victorious in a battle with his former ally Shang Tsung, Onaga returned. Even the combined might of Shang Tsung, Quan Chi and Raiden was not sufficient to defeat him. Raiden's desperate last measure was to use a self-destruct magic that released his godly essence, but that only succeeded in destroying Onaga's army and, presumably, the two sorcerers. Onaga was unaffected due to being resistant to all forms of magic and was now in possession of the amulet Quan Chi previously held.
It was at this time in which Shujinko, finally realizing he had been duped, took action. He traveled through the realms in order to find recruits to fight Onaga. All of these warriors came from extremely diverse origins but Shujinko planned to unite them to fight this enormous threat, who was now in possession of the six Kamidogu (found in the Temple background) and attempting to unite all of them into one.
Unbeknownst to Onaga, Shujinko had united many warriors and absorbed their fighting abilities, and was planning an attack on the Dragon King's stronghold. Shujinko had destroyed each of the Kamidogu, giving him the opportunity to eliminate Onaga. But as Shujinko landed the final blow, Onaga's soul was forced from Reptile's body and dragged down to the Netherrealm, where he was bound by Nightwolf. He remained there for a long time until he was discovered by Shinnok, who had also been trapped there. The fallen Elder God proposed that he would give Onaga his place at the Outworld throne in exchange for his help in returning his own power. Onaga reluctantly agreed, for the time being.
Shinnok informed Onaga about Blaze and the godlike power that would be given upon whoever defeated him in kombat. He proposed that the Dragon King join with Quan Chi, Shang Tsung, and Shao Kahn so that he may stand a better chance at attaining the power. Onaga did not trust Shinnok, and suspected that the former Elder God had something else up his sleeve. But with no other alternative to escape the Netherrealm, he accepted. Satisfied, Shinnok opened a portal to Outworld and sent Onaga back through, where he met with Quan Chi, Shang Tsung, and Shao Kahn and allied with them. He vowed that he would take Blaze's prize for himself, and would destroy everyone who ever stood in his way.
However, Onaga's desire for revenge against Shao Kahn proved to be greater than his desire to gain Blaze's prize. When Shao Kahn was knocked towards the edge of the Pyramid of Argus, Onaga grabbed him and flew far away from the pyramid. His former advisor managed to escape and return to the battle, leaving Onaga's final fate uncertain.
- Flight - Onaga flies with the great dragon wings upon his back.
- Fire Breath - Onaga can breathe streams of draconic fire or spit explosive fireballs.
- Necromancy - Onaga possesses many dark magical abilities, chief among them being the power to bring the dead back to life and control them like puppets.
- Invincibility - Onaga has proven capable of shrugging off magical assaults with ease and his age is also indeterminable. It could be that he does not age at all, but this is unconfirmed. Although he has also been resurrected on one occasion, Onaga is not truly immortal.