Back in the beginning of time, a dazzling light gave birth to the Great Dragon. It is an ancient creature, which was said to have fiery breath. This breath sparked the Dragon Fire (or Dragon Flame, Great Sacred Fire) that gave life to the whole Magic Dimension eons ago, spreading life, light, and heat across the universe. Eventually, the dragon became exhausted and chose to rest on a planet called Domino, which made it the most beautiful and harmonious world of all. Its mighty energy was later handed down to the royal family. Later in the series, the creature's history was further explored.
In the second season, it is said that the Shadow Phoenix, Lord Darkar, was created along with the Dragon at the same time. The said creature had the opposite power the Dragon has. It can absorb energy instead of giving life.
The third season also tells that it has an elemental opposite: Water Stars that has the ability to extinguish the Dragon Fire and vice versa. According to Tecna, the Dragon can be a symbol of good against evil.
The Great Dragon looks like a reptilian creature with a long serpentine body. It has only a pair of forelimbs in the Cinélume dub but in the Nickelodeon Specials and as from Season 5, it is seen with a pair of forelimbs and a pair of hind limbs. It possesses mustache-like tendrils above each nose and eyes and there are horn-like projections on its lover jaw. On each side of its head is a large triangular horn-like frill.
The Great Dragon's color is orange with a yellow aura around it, which gives its body a fiery lava-like look.
In Season 6, the Dragon has five heads with red eyes. All of it heads share one tail and has a purple aura.
According to Faragonda, the Great Dragon was born at the beginning of time from the dark void as a dazzling light and created the whole Magic Dimension with its fiery breath, where it spread life, light, and heat.
Later it became exhausted and chose its resting place on the planet Domino. Since then the royal heirs of the royal family of Domino have been the Guardians of the Dragon Fire, the present guardian being Bloom.
When Bloom does research in the library at Alfea, she finds in the books there that after the Dragon disappeared, the Magic Dimension was consecutively ruled by the nine Nymphs of Magix, all-powerful fairies who had controlled the destiny of the Magic Dimension and had been the previous Guardians of the Dragon's Fire (possibly implying that they were her ancestors), the last being Daphne, (Bloom's elder sister, even if she did not know it then).
When Darkar tried to gain control of the Ultimate Power, he sent his servants, the Ancestral Witches and Valtor, to claim the Dragon Fire from Domino, therefore causing the planet's destruction. When all the inhabitants of Domino disappeared in the final battle between the Company of Light and the Ancestral Witches, the whole Magic Dimension thought that the Dragon's Flame had been extinguished, until the Trix stole it from Bloom and revealed to her that it was still burning inside her, since she was its Guardian. This was confirmed when Bloom openly used the Dragon's Flame in the final battle against the Trix.
It is revealed that when the Great Dragon created the Universe, a small part of its Fire mixed with the Darkness, creating a kind of dark Dragon Fire which the Ancestral Witches found and fashioned into a man they raised as if he were their own son and named him Valtor.
It is possible that the part of Darkness which mixed with the Dragon Fire from which Valtor was created was in fact a small piece of Darkar's darkness, since it was stated that both the Shadow Phoenix and the Great Dragon both were born in the original void before the beginning of Time, which possibly means that they were born together at the same time, since in the first episode of the second season, Professor Wizgiz said, that in the Magic Dimension everything and every magic power has an opposite, also implying that opposite powers are created together.
In "Vortex of Flames," it is seen as Bloom is dropped down by Diaspro to the pit. The dragon and Bloom's dragon fight, but Bloom's dragon got defeated. Bloom finally gives one last effort to her dragon, and it defeats the Dragon. With Bloom's power restored and her success on passing the test, she earns her Bloomix and emerges from the pit.