Drona was a poor Brahman. He was student of Bharadwaj Muni. He and his friend Drupad who was the prince of Panchaal were among very good students. In Ashram Prince of Panchaal promise him to be his friend always even though he will become the king. After ashram life they got separate.
Drona got married to Kripi, sister of Kripacharya, the main Priest and teacher for Hastinapur's royal family. As Drona was always very ambitious and energetic he was never satisfied with an ordinary jobs. Once he listened that Parashuram is giving up his belongings to other Brahman. He also rushed to him.
"You are quite late. I already gave my all belongings except these weapons which no Brahman wants to take". Parashuram said. "I will be grateful to you if you give your weapons and their working technique" Drona said.
When he returned home, he saw his son crying and asking for milk. Kripi gave him mixture of rice powder and water. She was not able to provide normal milk to Ashvtthama, her son. Ashvtthama threw the pot and said that he wants the milk as all his friends drink. Kripi was not able to stop tears in her eyes.
Drona decided to go Panchaal, visit to his friend to seek some help from him. "Your friend want to meet you 'O' King" courtier said. Drupad saw a poor Brahman with a woman and a child in torn cloths entering in court. He could not tolerate to be called as a friend of such a person.
"Who are you" Drupad asked. "I am your friend Drona. We were in the same ashram under Bharadwaj Muni." Drona replied. "I don't remember you. How you can be my friend? I am a king, you are a poor man. Only a king could be a friend of a king. If you want some money, take and go away." Drupad said in very insulting tone.
I will remember you words always. Next time when we will meet, we will be equal. Drona left the court in anger.
It is very important for the Kshatriya that is the warrior clan to be proficient in archery and sword fencing. We already know that the Pandav and the Kaurava were being and brought up together by Bhishma. He always showed keen interest in their education and proficiency in warfare. He therefor wanted the best among the tutors to train Pandav and Kaurava in archery and sword fighting.
One day all the princes were playing the ball game together and the ball fell into a dilapidated well. How to take out the ball was their problem. Just at that time, the spotted a Brahman. He was a thin person but his bright eyes and the glow on his face indicated a brilliant man. The Brahman listened to the children and said in a teasing voice, You are from a warrior race and still you do not know how to take out the ball from the well!" The children were surprised. What is the relationship between the ball and the warrior race, they wondered. They raised this doubt with the Brahman. He replied, "Let me show you."
The Brahman was not an ordinary person. He pulled out a blade of grass and after chanting a mantra, threw it into the well. The grass hit the ball with lot of force and the ball bounced out of the well. The princes realized that he was an extraordinary man. They wanted to know his name. But Brahman smiled and said "Go to your grandfather Bhishma and narrate this incident to him. He will know who I am".
It didn't take long for Bhishma to know the identity of this Brahman. He was non other than Dronacharya. Bhishma had known that no one could match Drona's skill in archery in the entire land of Bharat. So Bhishma hastened to meet Dronacharya and appointed him as the tutor for the princes. All the princes felt happy and proud that they were Dronacharya's disciples.
Among all the princes, Arjun was Dronacharya's favorite disciple. Arjun always aimed his bow very well. He always respected his Guru. And though the other princes received good training from their master, it was Arjun who excelled himself in archery.
Dronacharya thoroughly taught all of them. He never forgot the incident happened in Drupad's court. Ever science this incident, Drona waited for an opportunity to teach lesson for Drupad's arrogance. With brave Arjun, With Duryodhan who was good at the mace, with the powerful Bheem and with courageous Yudhishthir as students, Drona felt that the time was right for him to seek his revenge against Drupad. So, first of all, he ordered Duryodhan to wage a war against the Panchaal king and drag him b the hair through the battlefield. But Duryodhan was no match for Drupad and was easily defeated by him. Disappointed Drona entrusted this task to Arjun.
It did not take long for Arjun to defeat Drupad. He imprisoned the King and produced him before Drona. Drupad felt punished. All the insults that he had heaped on Drona flashed through his mind. He stood before Drona with a bowed head.
Since Drupad was defeated in the war, Drona had the right to claim the entire kingdom as his own. But he was an unselfish person. So he told Drupad "My friend, let one half of the kingdom be with you. I will retain the other half so that both of us can be equals. Then you will have no hesitation in accepting me as your friend."This generous attitude of Drona made Drupad feel all the more humiliated. But instead of being grateful to him, a feeling of revenge grew strong in Drupad.