(Mostly from the Hyper Colleseum card game, not canon in the Digimon Quest continuity)
The Four Great Dragons are the most powerful of the Dragon Digimon, and are each connected to the primal forces also embodied by the Binaries, the Celestial Angels, and the Bringers of Sorrow.
Azulongmon is the eldest, and most powerful of the Dragons, and is also one of the Digimon Sovereign. As the Dragon of Faith, he is given dominion over the crests of Hope and Light.
Magnadramon is the Dragon of Light. She is also the caretaker of the Golden Digimental of Miracles. She is linked to the same powers as the Celestial Ophanimon.
Goldramon is the Dragon of Hope, and is linked to the same power as the Celestial Seraphimon.
Megidramon is the Dark Dragon of Dispair, a creature of fear and sorrow. He carries the Digital Hazard mark, and it is said that the Digital World fears for it's existance whenever he manifests.