Here are my thought on this. The dragon called were called to duty as heros to do heroic things. After the fall of blood the skies darkened people starved, plague was rampant, crime went through the roof, dictators ruled, and monsters encroached deeper into settled lands in search of food. The result of this was that many had to fight to stay alive and/or to protect those around them. There was a drive to become powerful to do that.
With so much turmoil many found themselves in dire circumstances and had to act. From this arose a new breed of "the powerful" (fighters, mages, clerics, bards...) not from the drive to be heros but the drive to survive. That type of upbringing (for want of a better word) created a generation of powerful beings that did not band together against a common foe but grew in power to serve other ends, some good some not.
Then the skys cleared and a new age of prosperity came about and in that new age the "survivor" grown powerful and the "leftover" dragon called opened schools and training halls. The existing schools and teachers that survived the dark times found more students coming to them. Many who were fueled by stories of heroic deeds, the freedom of the open road, a drive to make a mark in the world, or just to get their part of the new brighter times sought out adventuring as their path. From all of these things a generation of true adventurers was born.
So as I see it we have the dragon called, the dark ages survivors, and the true adventurers. In these types there are heros, villains, thrill seekers, treasure hunters, and mixes of the above.
