For me, the central fact about dragons is that they have hoards. Specifically, all adult dragons have one specific thing (including metaphysical concepts) that they hoard, that they covet, that gives them energy. A dragon in possession of a suitable hoard needs only very little mundane food, and that only if injured. Their energy comes through their connection to the hoard.

Young dragons usually have an idea of what their hoard will be, and are trying to build it as fast as possible. Which makes them brash and dangerous to those around them. When they gather enough, they metamorphose during an extended sleep period (years or more) into adults. Depriving an adult of his hoard is suicidal--it will take any means necessary to rebuild it or destroy you. Because you effectively cut off its food supply and thus pose an existential threat.

Examples of hoards that have come up are:
* A black dragon (now turned dracolich unwillingly) who hoards butterflies.
* His mate, a gold dragon, who hoards political influence.
* A white dragon who hoards magical items. Any magical item.
* Three dragons (a silver, a gold, and a bronze) who together hoard a particular city-state.
* A brass dragon who hoards stories of adventure. To the point that she "invites" interesting people into her den to hear their stories and to tell them her stories. Whether they want to attend or not. She always pays them well, but still. Part of her draconic name translates to "oh will she ever shut up?'[1]
* A gold dragon who hoards architecture. Buildings. Goes by the name "The Landlord". He doesn't care about people at all, as long as they maintain the buildings he considers his (which is all of them within his territory, a partially-ruined city). Uses paralyzing breath almost exclusively so as not to cause damage to structures.

[1] this one is a former player character, a dragonborn sorceress transformed into a true dragon via divine providence at the end of a campaign. She's one of the rulers of a particular city and generally a nice person. Except if she wants you to tell her a story and you try to refuse.