Karna was known as the son of a carpenter; nobody knew that he was the eldest son of Kunti, and a Ksatriya. This was not known until he died, and Kunti began to cry. Yudhisthira asked her why you are crying, he is the enemy, and she said, he was my first son. He was born out of her ear, so he was called Karna. When she was very young, she got some mantra which could be used to call any demigod, so just to try it, as experiment, to see if it worked, she called the sun god. He immediately appeared there before her, and said, I will give you the benediction of one son; she replied that she simply was experimenting with this mantra, that she did not want a son, and she became afraid as she was unmarried girl. He said I shall give you a son anyway, and it will be born out of your ear. So as she was virgin girl, she became very frightened that people may say things, so she put him into the ocean. Yes, Karna had many extraordinary attributes. He was a great soldier, and a most charitable man. He was so strong that it was not possible for Arjuna to kill him; he had to take unfair tactics and kill him. Karna could have killed Arjuna, but by Krishna's Grace, Arjuna killed Karna. In other words, Krishna killed Karna, otherwise, nobody could have killed him.