King Dhritrashtra of Kuru vansh (a family name) had hundred sons.Duryodhan was the eldest son. He was an avatar of the demon Kali who had bewitched the soul of Nal (King of Nishadh kingdom and husband of Damyanti), forcing him to gamble away his kingdom.
When Dhritarashtra's queen Gandhari's pregnancy continued for an unusually long period of time, she beat her womb in frustration, at the envy of Kunti, the queen of Pandu who had given birth to Yudhishtir, the eldest of the Pandavas. Due to the actions of Gandhari, a hardened mass of grey-colored flesh produced from her womb. Gandhari was very shocked and upset. She worshipped Vyas, the great sage who had blessed her with one hundred sons, to redeem his words. Vyas divided the flesh ball into one hundred and one equal pieces, and put them in pots of ghee, which were sealed and buried into the earth for one year. At the end of the year, the first pot was opened, andDuryodhan emerged.

Duryodhan means "hard to conquer". His chariot bore a flag depicting a hooded cobra. He had a sister named Dushaala.Duryodhan's body was said to be made out of lightning, and he was extremely powerful. He was revered by his younger brothers, especially Dushasan. Learning martial skills from his gurus, Kripa, Drona and Balram , he was extremely powerful with the mace weapon, and the equal of Bhima, the powerful Pandava, in its use.As they were born in Kuru vansh, all the brothers got the best of education. They got their education along with their cousins, the Pandavas.

At the martial exhibition where the Kauravas and Pandavas princes demonstrated their skills before their elders, their guru Drona and the people of the kingdom, a great and effulgent warrior, Karna appeared and challenged Arjun, who was considered by Drona to be the best of the warrior princes. But Karna was humiliated when Kripa asked him to ascertain his caste, as it would be inappropriate for unequals to compete.

Duryodhan immediately defended Karna and made him the King of Angadesh so that he is regarded as Arjun's equal. Karna pledged his allegiance and friendship toDuryodhan, asDuryodhan had rescued him from the source of continuing humiliation and hardship for him. Neither of them knew that Karna is in fact Kunti's eldest son born to Surya.

A very intense bond of friendship developed between the two, andDuryodhan became very close to Karna. It is held that if there was one good quality inDuryodhan, it was his deep affection for his friend Karna. It is said that,Duryodhan never had a tear in his eyes even when his real brothers got killed in the battlefield, but when Karna his beloved friend got killed he could not be consoled.
Although loved by all his family,Duryodhan and most of his brothers are seen as inferior to the Pandavas in their adherence to virtue and duty, and respect of elders.Duryodhan was mentored by his maternal uncle Shakuni, who desired the elevation of his sister's children at the expense of the Pandavas. Shakuni masterminded most ofDuryodhan’s plots to humiliate and kill the Pandavas.

Duryodhan and his cousin Bhima had learnt the art of mace from Krishna’s elder brother Balram . Bhima had expertise in the art of mace and soDuryodhan was jealous of him. He once tried to kill Bhima by poisoning his food. He had built Laksha-griha (house made of lac), so that he can put it on fire and kill the Pandavas inside it, but somehow Pandavas came to know about this plan and were saved. After this,Duryodhan along with his uncle Shakuni organized a game of gamble and deprived Pandavas of everything by cheating them. Pandavas had put their wife Draupadi in gamble and lost her to Kauravas. When Dushasan brought Draupadi in the courtroom,Duryodhan made her sit on his lap (thighs). Bhima was so angry at this gesture that he vowed to breakDuryodhan’s thigh bones with his mace.

According to the terms and conditions of the game, Pandavas went for exile (residing in forest) and were living incognito for one year. After completing their punishment, when they returned to their kingdom and asked for their share,Duryodhan did not even agree to give land as small as a hole of a needle also. Shri Krishna, as a messenger of Pandavas tried to convinceDuryodhan but did not succeed. At the end, the war of Mahabharata was fought on the grounds of Kurukshetra.

Duryodhan went to the city of Dwarka seeking Krishna’s support in the battle that was to be fought against the Pandavas. But he found Krishna asleep. So he sat close to the head of Krishna’s bed, waiting for Krishna to wake up. Arjun arrived there soon after and, finding Krishna asleep, he too waited for Krishna to wake up, but he chose to sit at the foot of Krishna’s bed. When Krishna woke up, he saw Arjun and asked, “What do you want?” “Hold on,” thunderedDuryodhan, fearing that Arjun would ask for what he had come to Dwarka for, “I came here first so you must ask me that question first.” “Maybe you did,” said Krishna sweetly, “Nevertheless I will ask Arjun the question because when I woke up I laid my eyes on him first. You should have had the humility, or the intelligence, to sit at my feet if you sought favors from me. But do not fear; you too shall leave with what you desire.” Then turning to Arjun, Krishna asked, “What do you want – my army or me?” Without a moment’s hesitation, Arjun replied, “You, Krishna, only you.”Duryodhan heaved an audible sigh of relief. For he had come to Dwarka wanting Krishna’s army and, as Krishna promised, he got what he desired. In the endDuryodhan lost the battle even though he had eleven armies on his side. The Pandavas only had seven but with Krishna on their side, they also had intellectual capital that allowed them to skillfully maneuver their limited material resources so as to obtain maximum and definitive results.

After a couple of days of fighting, most of the Kauravas had been destroyed with the exception ofDuryodhan and a few others. Queen Gandhari was distraught when she heard that all her sons exceptDuryodhan had been slained. Despite knowing thatDuryodhan was wicked and his cause unrighteous, she decided to help him win. Asking him to bathe and enter her tent naked, she prepared to use the great mystic power of her eyes, blind-folded for many years out of respect for her blind husband, to make his body invincible to all attack in every portion.

But when Krishna, who was returning after paying the queen a visit, ran into a nakedDuryodhan coming to the tent, he mockingly admonished him for his intent to appear so before his own mother. Knowing of Gandhari's intentions, Krishna criticizedDuryodhan, who sheepishly covered his groin before entering the tent.
When Gandhari's eyes fell uponDuryodhan, they mystically made each part of his body invincible. She was shocked to see thatDuryodhan had covered his groin, which was thus not protected by her mystic power.

Duryodhan ran away once he saw his army men being slained by the Pandavas. The Pandavas set out in search ofDuryodhan but could not locate him as he was hiding in the waters of a lake.

On finding him, the brothers stood at the banks, taunting him and challenging him to come out and fight like a man.Duryodhan said that it was wrong for them to challenge him all together as he had no weapon and was all alone. He said that he would be willing to fight as long as they provided him with a weapon and fought him one by one.

Upright, kind-hearted and generous Yudhishtir agreed to give him the weapon of his choice as well as the combatant of his choice and the entire kingdom back if he won. Lord Krishna was furious at this foolish offer and another game of chance. He also knew thatDuryodhan was the first among equals in the use of the mace and Bhima might not have much of a chance. So he advised him to strikeDuryodhan below the navel. Krishna knew that this part ofDuryodhan’s body was not invincible. Even though this was against the rules, lord Krishna explained that even the gods had to resort to trickery when they fought the demons to ensure that good won over evil. In this way Bhima was able to secure a resounding victory overDuryodhan.

All the Kauravas were killed in this war. At the end of Mahabharata, Bhima attackedDuryodhan’s thighs with his mace and fulfilled his oath by killing him.

Duryodhan was one of the main reasons why the war of Mahabharata was fought. His vices of greed and jealousy resulted in fighting with his peace loving and gentle brothers and resulting in the murder of his entire clan.