Originally posted by: Wistfulness
The Mahabharata explicitly states that Duryodhana was a part of demon Kali, and all his brothers were demon incarnates. It's also stated that Duryodhana would be the exterminator of the Kuru race. This is something that's skipped by tv serials.
The evil-minded and wicked king Duryodhana, the destroyer of the fair fame of the Kurus, was born of a portion of Kali on earth. He it was who caused all creatures to be slain and the earth to be wasted; and he it was who fanned the flame of hostility that ultimately consumed all. They who had been the sons of Pulastya (the Rakshasas) were born on earth among men of Duryodhana's brothers, that century of wicked individuals commencing with Duhasasana as their first. And, O bull among the Bharata princes, Durmukha, Duhsaha, and others whose names I do not mention, who always supported Duryodhana (in all his schemes), were, indeed, the sons of Pulastya. And over and above these hundred, Dhritarashtra had one son named Yuyutsu born of a Vaisya wife.'
ADI PARVA
^ Here the destruction of the Kurus is attributed to Duryodhana.
"Know that Duryodhana was Kali, and Sakuni was Dwapara"
ASRAMAVASIKA PARVA
Moreover, there were several ill-omens that followed Duryodhana's birth and his physically/morally blind father was advised to abandon him for the kingdom's sake.
As soon as Duryodhana was born, he began to cry and bray like an ass. And hearing that sound, the asses, vultures, jackals and crows uttered their respective cries responsively. Violent winds began to blow, and there were fires in various directions. Then king Dhritarashtra in great fear, summoning Bhishma and Vidura and other well-wishers and all the Kurus, and numberless Brahmanas, addressed them and said, 'The oldest of those princes, Yudhishthira, is the perpetuator of our line. By virtue of his birth he hath acquired the kingdom. We have nothing to say to this. But shall this my son born after him become king? Tell me truly what is lawful and right under these circumstances.' As soon as these words were spoken, O Bharata, jackals and other carnivorous animals began to howl ominously And marking those frightful omens all around, the assembled Brahmanas and the wise Vidura replied, 'O king, O bull among men, when these frightful omens are noticeable at the birth of thy eldest son, it is evident that he shall be the exterminator of thy race. The prosperity of all dependeth on his abandonment. Calamity there must be in keeping him. O king, if thou abandonest him, there remain yet thy nine and ninety sons. If thou desirest the good of thy race, abandon him, O Bharata! O king, do good to the world and thy own race by casting off this one child of thine. It hath been said that an individual should be cast off for the sake of the family; that a family should be cast off for the sake of a village; that a village may be abandoned for the sake of the whole country; and that the earth itself may be abandoned for the sake of the soul.' When Vidura and those Brahmanas had stated so, king Dhritarashtra out of affection for his son had not the heart to follow that advice.
^ This is one of the reasons I deem Dhitarashtra the main villain. By succumbing to personal attachments he proved himself morally unworthy too.