Tai lung was the adopted son of Master Shifu, who had raised and trained him under the impression that he was to become the prophesied Dragon Warrior one day. But after he was denied the title by Grand Master Oogway, he revealed his true dark nature by rampaging the Valley, resulting in his incarceration for twenty years. Despite all the strength his inner rage had given him since then, he finally met his match when he was defeated by the true Dragon Warrior.
Tai Lung was shown to be dark, cynical, and overall evil in nature. In the past, when he was raised and trained by Shifu (who was a young adult at the time), he seemed to be a happy, sweet, energetic, playful little snow leopard with much dedication to the arts of Kung Fu and was viewed as a great Kung Fu prodigy in the eyes of his loving master.
When he completed his training by mastering all one thousand scrolls of Kung Fu, Tai Lung (who was now an adult) was seen as a strong-hearted individual with obvious fierceness and strength in both his eyes and body. However, his ever-growing pride Grand Master Oogway found was the reason that Tai Lung was not made the Dragon Warrior, which was his aim in life. Expecting his master to speak for him on his behalf, Tai Lung received yet another emotional blow when Shifu was too reluctant to say something for him. It was this double denial that revealed the leopard's dark and true nature of his heart. His pride turned to corruption, which finally bubbled over when he rampaged the Valley of Peace.