In Chinese folk tale, there was a rumor saying that the Chinese primogenitor was a human with a dragon body. That is the reason why we say that Chinese people are the offspring of dragon.
It is said that dragon can ask for wind and rain, which means it has the power to control the nature, so many Chinese people worship dragon till now. It also became the symbol of authority. Chinese emperors always put nine dragons on their clothes to show their authority and power. People with power in the old days such as the family member of the emperor could also put dragons on their clothes but they were not allowed to do so without the king's approval. Plus, they could not put nine or more than nine dragons on their clothes as it was the symbol of the king. If they had nine dragons on their clothes, they would be killed.