Drona and Drupada were great friends during their childhood days. However, they later became enemies. This is an important story in the Mahabharata and it had far reaching consequences. Drona and Drupada were students of Bharadwaja. During the time of education both Drupada and Drona became great friends.
Drupada was the son of King Prsata, who ruled Panchala. Drona was a poor Brahmin.
When they were students, Drupada had promised Drona that he would help him financially when he becomes the king of Panchala.
After education, both returned to their respective places. Drona became a great archer but remained poor. He got married and had a son, Ashwathama. He found it difficult to make both ends meet. Fed up with poverty, Drona one day approached Drupada who was now the king of Panchala.
However, King Drupada did not care to recognize Drona as a friend. When Drona tried to remind him of their friendship, Drupada insulted him.
Drona then vowed to avenge the insult.
Drona then became the teacher of Kauravas and Pandavas. As Guru Dakshina, he asked his students to tie up King Drupada with a rope and bring before him.
The Pandavas defeated King Drupada and his army and fulfilled the wish of their teacher.
Later, Drona pardoned Drupada and released him.
But Drupada did not forget the insult and he performed a yajna. He received two children at the end of yajna – a son (Dhrstadyumna) and a daughter (Draupadi). Dhrstadyumna finally killed Drona in the Mahabharata war.