Drona was born to Bharadwaja. As per his father’s instructions, Drona married Kripi, the daughter of Sharadwa. Ashwathama was born to them, as per Mahabharata Adiparva Chapter 130.

As soon as he was born, the child made a sound similar to Uchaishravas. A divine voice said that the child should be named Ashwathama since he made a sound similar to a horse, as per Mahabharata Adiparva Chapter 130 verses 48-49.

Ashwathama learned the art of weaponry from his father. Drona himself was learning from Parashurama then. He later became the guru of the Pandavas and Kauravas. Ashwathama continued to learn with them, as per Mahabharata Adiparva Chapters 52-64.

Drona wanted to teach his son Ashwathama some special lessons. He started sending all the princes and his son to fetch water daily. Ashwathama always got back earlier than the others, and before the others reached, Drona used to teach his those lessons. Arjuna understood this and used the Varunastra to fill up the pots fast and return with Ashwathama. As per Mahabharata Adiparva Chapter 132 verses 17-19, Drona then taught them both the special lessons.

Ashwathama was present at Yudhishtira’s Rajasuya as per Mahabharata Sabhaparva Chapter 34 verse 3. Ashwathama then appears in the Mahabharata only in the war. He plays a crucial role on the 18th day of battle.

During the war, he killed Nila, Anjanaparva, Suratha, Shatrunjaya, Balanika, Jayanika, Jayashwa, Shrutahva, Hemamali, Vrishadhra, Chandrasena, the ten sons of Kuntibhoja, Sudarshana, Vridhakshatra, Malayadhwaja, the king of Chedi. He also defeated Shikhandi, Abhimanyu, Virata, Satyaki and Vindhya. As per Mahabharata Dronaparva Chapter 139 verse 121-123, he was once defeated by Arjuna. But he once stunned Krishna and Arjuna using Aagneyastra. He became commander of the Kaurava army twice. After the war, he killed the Panchalas and their attendants while they were asleep in their tents.

Dhrishtadyumna, son of the Panchala king, killed Drona. Ashwathama was enraged on hearing this and reached the Pandava camp. He was accompanied by Kripa and Satwata. As he was about to enter the tent, a terrifying spirit appeared in front of him, but he was unfazed and fired arrows at it, as per Mahabharata Sauptikaparva Chapter 6 verses 2-19. The spirit seemed to swallow the arrows. Ashwathama prayed to Shiva, who appeared and gave him divine swords. Ashwathama entered Dhrishtadyumna’s tent and woke him up by nudging him with his leg. He then beheaded  Dhrishtadyumna.

After killing Dhrishtadyumna, Ashwathama invoked the Brahmashirastra to kill all the Pandavas. Arjuna countered it with one of his own, which ironically, was given to him by Drona. Sages were aghast on seeing this display of weapons and Vyasa, along with a few others tried to get both of them to call back the weapons. Arjuna agreed to do so provided Ashwathama gave them the jewel that adorned his forehead. This jewel contibuted a lot to Ashwathama’s valour, and so he declined, as per Mahabharata Sauptikaparva Chapter 15 verses 28-30. But in the end, he agreed to give the jewel, however refusing to withdraw the weapon. The astra flew towards the womb of Uttara, Abhimanyu’s wife. Once, when the Pandavas were living in Upaplavya, an old brahmin had said, looking at Uttara, that towards the end of the Mahabharata war, she would have a baby and it would be tested in the womb, and so it should be called Parikshit. Seeing the astra, Krishna said that thought he child would be killed, it would be reborn. He also told Ashwathama that he would be known as a child killer, and though he would pay for this by having to roam the earth for three thousand years without anyone acknowledging him. Further, Krishna said, he would be plagued by diseases, while Parikshit would become a renowned king and would rule the land for a long time. Saying that, Krishna revived Parikshit and Vyasa supported this. Ashwathama was remorseful, gave the jewel to the Pandavas and followed Vyasa into the jungles, as per Mahabharata Sauptikaparva.

Ashwathama is also known as Acharyananda, Acharyaputra, Acharyasuta, Acharyatanaya, Acharyasattama, Drauni, Draunayani, Dronaputra, Dronasunu, Guruputra, Gurusuta, Bharatacharyaputra.