The Dragonborn

In the final years of the dragon wars, the Elven Magi began magical experiments to breed a race of dragon men as soldiers. They gathered dragon eggs of every kind (metallic and chromatic) and wove elven embryos into the eggs. What emerged was a hybrid creature with traits from both elves and dragons. The first 20 (10 male and 10 female) dragonborn emerged from their eggs with the same general appearance, elemental resistance and dragon breath as their draconic heritage in a humanoid shape. They lacked tails or wings and reached physical maturity within 15 years, but proved to be as long-lived as their elven ancestors. The Elves designed them to be able to reproduce with each other, but not other creatures (to satisfy the growing purist natures of the elven magi).
These dragonborn never served their purpose, as the dragon war ended before most reached adulthood. The Sydonian King Arvald Reeve suggested that the dragonborn should be destroyed, but the Elven mages instead freed them and exiled them into the world.
In exile, the dragonborn progenitors largely stayed together for a time. They had been raised in couplings of the same type to avoid diluting their draconic traits, and while some remained in those couplings into adulthood some found mates among those unlike them. The chaotic forces behind their magical origins, however, led to completely random outcomes when the first dragonborn children were born. The red dragonborn progenitors gave birth to a silver dragonborn, and those who mixed were as likely to birth similar children as those who had not. Random draconic traits also became more common with each generation, with some dragonborn born with tails and even wings.
Like their elven ancestors, the dragonborn felt the passing of the world more slowly, and their emotions were heightened. They felt loss more strongly, loved more passionately and hated more intensely. They mated for life, and were unlikely to mate again after the passing of their loved ones. Like their draconic ancestors, they found themselves drawn to the land that once suited their ancestors best. Thus did the dragonborn live largely in seclusion in the forests, caves, and mountains of the world. They avoided men and elves, and kept to themselves. For the hatred men shared for dragon kind extended to them as well, and they found themselves often persecuted.
In the centuries that followed, the dragonborn came to be accepted and integrated into Sydonian society (though as second-class citizens, still often persecuted) as the hidden corners of the world became rarer. Dragonborn adventurers were common in the age of heroes, and their mages joined the Arcanatorium and other places of learning. Though the dragonborn had been largely agnostic since their creation (not owing their creation to any divine entity), some came to adopt Sydonian faith. Others who studied with metallic dragons adopted the worship of Bahamut, broodmother and goddess of all metallic dragons. They formed the temple of Bahamut, along with a knightly order tasked with defending the world from evil dragons (sometimes even from overzealous metallic dragons). The temple accepted all goodly dragonborn, regardless of their draconic traits. Likewise, some dragonborn came to follow Tiamat and joined cults worshiping the evil broodmother of chromatic dragons.