The Three

The Three are powerful evil dragons that have decided to work together to achieve their common aims. They are of course constantly plotting against each other, because what's the point of strength if not to sharpen itself?

The Red hoards destruction, and all destruction flows through him. He watches the Emperor's moves with great interest, these days. It is posited that the Red has hidden his own destruction within his hoard, to make himself invulnerable.

The Blue hoards magic, and all magic flows through her. She'd very much like to claim power over the Instrumental University for herself - the Department of Mysticism and Metamagic has a vacancy for this very reason, - but its headmaster is holding out on her appointment.

The Black hoards secrets, and all secrets flow through them. The Fishermen dance to their tune.

The Three, Once Five

The White was murdered by the Lich King. This freed its hoard of entropy, which was magically captured, and members of the Undying Peerage are thought to deposit their own deaths and decay into it to this day.

The Green was imprisoned by the Elf Queen. This freed its hoard of pattern, or self-similarity. This is the property of living things that makes chickens produce eggs which produce chickens, and not say, basilisks. Things that grew around the Green tended not to grow into what they ought to be. All druids who use shape-shifting magic rely on this resource.

Thus the hoards of the White and the Green were seized by the undead and fey, respectively. It has been posited that these modes of existence were not viable prior to the ancient dragons' subjugation.