The dragon is called the Naga in Sanskrit.  Some poisonous dragons harm living beings.  The sea dragons can create great storms in the sea while the heavenly dragons protect the heavenly palace. In the Dharma Flower Sutra, there were eight great Dragon Kings who were the leaders of other dragons. Even though there are so many kinds of dragons, we seldom have a chance to see them. From the ancient time till now, there were many legends about the dragons in China and India. The Chinese call themselves 'The Heir of the Dragons', so we can never deny the existence of dragons.
     In former lives, the dragons had cultivated all types of blessings so they possessed the spiritual power to reveal themselves orto hide their forms as they wished. But as they did not uphold the precepts in former lives, and got angry easily besides being improper-minded, stubborn and contentious, they were born as dragons.  The dragons had to undergo the retribution of being burnt by hot sand.  Their palace clothing were often blown away and they were eaten by the Golden Wing Garuda.  So they also wished to leave the form of dragons and be born in a good dwelling.