Naga is a rogue Bakugan and one of the White Ones who tried to control all the power in Vestroia. In order to do so, he tried to absorb the two opposite cores, but made a mistake and trapped himself within the Silent Core, while the Infinity Core was expelled to Earth. At the same time, Naga shot energy waves to brainwash the Bakugan, which altered the dimensional balance and created the Doom Beings. He is the main antagonist of the first season of the anime, partnered with Hal-G a few times.
Naga and Wavern were born during the Great Revolution, as they became trapped in the empty space between dimensions. When Drago was able to get across from his Pyrus Space, he could meet them both, but Naga only cared about himself and was angry for being born powerless. He tried to go to the center of Vestroia to get the powet of both Cores, despite Drago's warning, but failed and accidentally created the shockwave that caused a strange phenomenon on Earth where cards fall from the sky and the Bakugan transporting themselves to the human world. After Dr. Michael went to Vestroia by accident, they met each other for the first time. Michael explained to him about the Dimensional Transporter, unaware about his true motives. At last, Naga expelled Michael back to Earth and used a Dimensional Transporter Card he got from him to succesfully enter the center of Vestroia.
After transporting himself to the center, Naga attempted to capture the powers of the Silent Core and Infinity Core, sources of negative and positive energy respectively of Vestroia, by going to them directly and absorbing them to fulfill what he believed to be his destiny. He failed, however, and was unable to control the power of the Silent Core, only being able to absorb the Silent Core after it trapped him inside; after that, catastrophic energy surge was caused due to the huge amount of negative energy was released and the Infinity Core became bonded to his twin sister, Wavern, who was sucked into a portal to the human world.
This disaster caused the negative energy to spill all over Vestroia and the Earth, including the Bakugan on Earth, and created Hal-G and Masquerade from the unsuspecting Dr. Michael and Alice, who were exposed to excessive negative energy when Naga absorbed the Silent Core. He used them both to hunt for the Infinity Core from Wavern and also supplied them powerful abilities like Doom Cards to send fallen Bakugan to the Doom Dimension. As a result, Masquerade frequently encounters the Bakugan Battle Brawlers, who are also after the Infinity Core to protect it from Naga. At the season finale, he was sent to the Doom Dimension while Drago became the Perfect Dragonoid and transformed himself into the new core for New Vestroia.
Many characters mentioned Naga, even though he isn't seen. It is revealed his actions also caused Bakugan to fall to Vestal, like they did on Earth.
And in the Legacy, he is one of the Bakugan that Barodius uses, along with Dharak.
And he is voiced by Frank Welker in the English dub and reprised by Hideyuki Umezu in the Japanese dub.