He is a skeletal, evil, split-nosed (with a seeming cleft lip and palate), wyvern Bakugan who was an outcast due to the fact that he and his twin-sister Wavern were not aligned with any of the six regions of Vestroia; they were known as The White Ones. He has no attribute, but pop-up effects are similar to Darkus Bakugan. He corrupted Alice Gehabich and Dr. Michael and created Masquerade and Hal-G, and leads them in his quest to take both the Silent Core and the Infinity Core, and gain the power to take over the entire universe.
He is the most power-hungry Bakugan (to be nearly matched by Dharak/Razenoid in the third and fourth seasons). Also, he is the only main villain to be a Bakugan without a brawler, even though Hal-G is technically his brawler (however it can be said in reverse to many cases of evil partnerships/relationships where it is the Bakugan not the brawler who is dominant). Naga has also a deep hatred for the Battle Brawlers, especially for Dan and Drago (he is the reason they met each other in the first place).
Naga and Wavern were born during the Great Revolution (the conflict turned into distortion, created by the original Dharaknoid and Dragonoid), 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. 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 Dr. Michael to go to Vestroia's center, where the Cores were located.
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; a catastrophic energy surge was caused due to the huge amount of negative energy that 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 as well as creating Hal-G (from Alice's grandfather, Dr. Michael) and Masquerade (from Alice) from two unfortunate people, who were exposed to too much negative energy when Naga absorbed the Silent Core. He used them both to hunt for the Infinity Core from Wavern thus encountering the Bakugan Battle Brawlers, who were after the Infinity Core as well, to protect it from Naga. Naga also created the Doom Cards for Masquerade, to send all fallen Bakugan to the Doom Dimension. At the first season finale, he was sent to the Doom Dimension (according to Bakugan.com) while Drago became the Perfect Dragonoid and transformed himself into the new core for New Vestroia. In Season 2, many characters mentioned Naga (or what he did) even though he is not seen.