Though The Eternals viewed their world as complete, Deos did not. He wanted there to be creatures that work the world. He wanted there to be things that do more an just eat, kill, and multiply. He wanted things that explore, and wield power similar to his own.
As the Eternals bask in the perfection of their world, Deos feels it to be incomplete. He loves sharing it with his children, but for them, there is nothing more to explore, as they were the ones who aided Deos in making it. The beasts that his fourth, and fifth children had made have no desire, nor the intellect to explore the world around them.
The beasts that Deos would make were quadrupedal, and reptilian. Each one with a sharp, angular snout, and horns facing back from their heads. With four total wings, he gave these beasts flight. With the metals beneath the soil, he gave them scales. The males of the species would have scales colored gold, red, green, or copper. The females silver, blue, and black. He gave these beasts breath as their tool which they could use to shape things to their desires. He pulled the fires of the world's core, and used it to give the males breath of fire. From the peaks of the mountains, he pulled the snow, and ice, and bestowed it unto the females, giving them breath of ice.
When these beasts awoke, Deos gave them the opportunity to name themselves. They called themselves Dragons. They pledged themselves to their creator, and assumed the role of his servants, to work the world he had laid forth for them. He saw the determination, and conviction of the dragons, and knew they were good.