Mahabharat

Karna

Who was Karna?
When Kunti tried to experiment Sage Durvasas mantra and called upon Surya Dev (Sun God), Karna was born.
She was to ashamed to keep him, wrapped the kid in a basket and left in river flow.
Fate took this kid to her future husband Pandus kingdom Hastinapur and Dhritarastra's charioteer and he and his wife Radha brought him up.
He was called Radhey and was later renamed to Karna by Dron.
He was destined to fight against his brothers.

What is his role in Mahabharata before the battle?
He wanted to learn from Dron but Dron returned him empty handed.
Since Dron had promised to make Arjuna the best warrior, Karna challenged Arjuna, probably to prove Dron was not the best teacher, and Arjuna not the best archer.

An insulted Karna swore to defeat and kill Arjuna one fine day.

Karn was so deep in debt of his friend that he didn't stop his friend from doing wrong things, and supported him some times,
like not opposing on trying to burn them alive,
When Duryodhan cheated Pandavas in dice Karna encouraged him and made fun of Pandavas and their wife.
Arjuna swore to kill Karna.
When Duryodhan went to make fun of Pandavas, he accompanied him.
When Duryodhan went to reveal Pandavas in Virat yudh and send them to another 12 years of forest stay and 1 year of hiding, Karna supported him.

To get a chance to fight Arjuna, he tried to foil any attempts of peace offering made by Krishna.

What is his role in Mahabharata in the battle?
Bhism knew that he was a Kaunteya (son of kunti).
With himself, Dron, and several other warriors, they already had a unbalanced battle field.
So he put a condition that Karn will not enter the battle field while the army fights under his supervision.
So Karna entered the field only after Bhism was incapacitated.
He showed his capabilities under Dron's supervision, killed Arjunas son, Abhimanyu with others.

Before battle, Indra came in disguise of a Brahmin and asked him his golden Armor and earrings.
Despite being warned by Sun god, not to give them, he gave them.
In return he received Shakti Astra (an astra which would surely kill its target) which he could use only once.

Bhim's son Ghatotkach, a demon, came to the battlefield, and played havoc on Kuru army, and Duryodhan. Duryodhan urged Karn to use the Shakti Astra on Ghatotkach. Karn had no choice but to kill Bhim's son as well.

After Dron was killed, he was made the general/chief.
He promised to kill Arjuna (he had vowed to Kunti, his mother, that she would have five sons after the battle, and either Arjuna or he would die)
He defeated other Pandavas and left them.
He fought Arjuna, but the curses he had received, took a toll on him.
He forgot all that he had learned, had no astras to use.
His chariot got stuck in a pit.
While he unmounted to free his chariot, Krishna urged Arjuna that since Karna had killed Abhimanyu when he was option less, he receive a similar fate.

Arjuna shot him.