Ashwathama
Aswathama was the son of a angry Brahman called Drona, who was seeking revenge for a humiliation at the hands of his childhood friend, Dhrupad, who was king of Panchal now. Ashwathama's father took to acquiring knowledge of warfare and to making himself powerful. He loved his son, but he loved his disciple Arjuna more, because he spoke in his tongue, he reflected his desires for mastery over warfare.. in short, he was closer to being his reflection than Ashwathama perhaps was. Sun/son..many a father thinks he is the sun, and wants to see his grandeur, reflected in his child, so he can enjoy a greater sense of self. He wants to leave himself in the world, when he passes on.. Ashwathama had to live with the knowledge that Drona saw himself better reflected in Arjuna.
No story turns too simply though. Drona tried little manouveres when he taught the prices, to grant his son more than what he would grant the others. But Arjuna would always out manouvere him: One day Drona sends the princes with pots to fetch water, saying whoever will come back fastest will get some special knowledge. He gave Ashwathama a pot with a wide neck. But Arjun, using his diverse knowledge of water and weapons, managed to return first.
In the battlefield of Kurukshetra, the alingments made Drona supervise the ruthless killing of Arjun's beloved son, Abhimanyu. And Ashwathama.. Drona became a father for the moment when he heard Yudhistira's voice announcing "Ashwatahama is dead'. He faltered, and is killed by Dhishtidhyuma