Karna was born to the Hindu Sun God Surya and Pritha(Kunti),the mother of the five Pandavas.
Rishi Durvasa,impressed by Pritha's devotion and helpful nature gave her a boon to get children with divine qualities from a desired god(s) and warned her to use it carefully.
To test the boon, she called forth Surya Dev.
Bound by the mantra,Surya Deva had to give Pritha, a child of divine origin.He blessed Karna to be a great warrior and gifted him the divine Kavacha and earrings soaked in Amrita,the nectar of immortality.
Due to her(Pritha's)fear and shame of giving birth to a child before marriage,Pritha abandoned Karna.She put him in a basket and left the basket afloat a raging river.
He was adopted by a Suta couple and came to be known by the name/as Vasusena.
Desiring to learn weaponry, he lied to Bhagwan Parashurama that he was of Brahmana lineage(Parashurama only taught Brahmanas and Kshatriyas/Demigods).
One day,Vasusena's's deception came to light.
Parashurama cursed Vasusena to forget the knowledge he acquired/Brahmastra when he battles his equal and needs it the most.
After that,Vasusena left Parashurama's hermitage with the Bow of Victory/Vijaya Bow gifted to him by Bhagwan Parshurama
After that he came back to Hastinapura and had a duel with Arjuna(Kalapradarshan).The fight was postponed due to (the)sunset.
Vasusena pledged lifelong loyalty to Duryodhana,the cousin of the five Pandavas as Duryodhana gave him the opportunity to battle Arjuna and had made Vasusena the king of Anga.
Due to the humiliation he faced in the Swayamwara of Draupadi,the princess of Panchal and his consequent defeat in battles, Vasusena was furious.
He encouraged Dushasana to disrobe Draupadi during the dice game and called her a whore(clarification needed).
Bhima had defeated Vasusena during Yudhishthira's Rajasuya Yagna.
Karna had fled from the battlefield during a war(Battle with the Gandharvas).
After Dronacharya's death,Karna was appointed as the commander- in- chief of (the)Hastinapura army.(He didn't participate in the war for some days due to his oath that he would only enter the battlefield after Bhishma was defeated or killed).
Vasusena donated his divine Kavacha to Indra Deva, the God King and received a weapon capable of killing Arjuna in return.
He used this weapon on Ghatotkach, the son of Bhima when Ghatotkach attacked the
Kaurava camp.
Karna had also promised his mother,Kunti, that she will always have five sons and that he will only use divine arrows of the same origin against Arjuna only once.
On the 17th day of the war,Karna was killed by Arjuna when he was distracted (The Brahmana's curse) while trying to lift his chariot's wheel which got stuck(Goddess Prithvi's curse).Karna, due to Bhagwan Parashurama's curse had forgotten the knowledge of summoning divine arrows for a short period of time.
Karna was a brave warrior.
But he met his end because he fought for adharma/the wrong side.
Achilles(Iliad) and Karna(Mahabharata) share some common characteristics.
Nowadays,Karna is seen as a flawed good man.
Some people conveniently forget his wrongdoings while some glorify him too much.
He was probably one of the most complex
characters found in Mahabharata.
Karna's tale is awe-inspiring and cautionary in nature.