King Santanu built up a reputation for being wise, virtuous and truthful.. He ruled the whole world from Hastinapura, the capital of the kings belonging to the Kuru dynasty. Kings of the neighbouring countries lived without fear since Santanu, the emperor, never troubled them.
One day, when Santanu was pursuing a deer he had struck with an arrow on the banks of the Ganges, he was amazed to find that the river had become shallow at one place. Then he noticed a young man of strong build and beautiful appearance keeping the river in check using his celestial weapon. The youth was none other than Shantanu’s son Devavrata. While Devavrata had recognized Santanu, Santanu couldn’t recognize his son immediately.
Presently, Devavrata vanished from Santanu’s sight. It then struck Santanu that the youth he just saw was his own son. He mentally appealed to his wife Ganga to show him his son. Responding to his appeal, Ganga appeared along with Devavrata and presented the young man to his father. “Oh king, here is your son Devavrata. He has learned the Vedas from Sage Vasishta. He has also been trained in the use of weapons. He has acquired all knowledge about the duties of a king. I am handing him over to you as per my promise.”
Ganga took leave of Santanu. Santanu took Devavrata to his palace, introduced him to his ministers and others and installed him as his heir-apparent.
Four years after this, when Santanu was hunting on the banks of Yamuna, he perceived a sweet fragrance. When he went in pursuit of this scent, he found that the fragrance was emanating from a young woman of exquisite beauty. Santanu went to her and asked her who she was. She said that she was Satyavati, the daughter of the Chief of the fishermen and that she was engaged in carrying people across the river on a boat.
Santanu met the Chief and sought the hand of his daughter in marriage. The Chief said that he would be glad to get his daughter married to Santanu, if Santanu gave a pledge that the son born to his daughter would be Santanu’s successor for the throne.
Unwilling to accept this stipulation, Santanu left for his palace. However, he was unable to forget Satyavati, the fisher woman of exquisite beauty. He was in a melancholy mood always. Noticing this, Devavrata asked his father the reason for his somber mood. Santanu replied, “You are my heir. I am not interested in marrying again. But the scriptures say that having one son is equivalent to having no son at all. You have been engaging yourself in valiant acts. You may get killed in a battle. I am worried about what will happen to the Bharata race, if something were to happen to you.”
Devavrata, being an intelligent person realized that his father had been facing a dilemma which he was reluctant to share with him. He asked the King’s ministers whether they knew what the reason for the king’s grief was. The minister who accompanied Santanu when he met Satyavati’s father told Devavrata about the king’s desire to marry Satyavati and the condition stipulated by her father for getting her married to the king.
Devavrata, accompanied by some Kshatriya chiefs, went to the Chief of fishermen and requested him to give his daughter Satyavathi in marriage to his father Santanu. The Chief reiterated his condition that the son born to his daughter should ascend the throne.
Devavrata then took a vow that he would abdicate his right to the throne in favor of Satyavati’s son. The Chief appreciated Devavrata for his sacrifice and said, “I have no doubt that you will keep your word. But how can I be sure that your sons won't stake a claim to the throne?’
Hearing this, Devavrata said, “Right at this moment, I take the vow of Brahmacharya (celibacy). I will not marry or beget children as long as I live.”
Once Devavrata uttered these words, flowers were showered on him from the heaven by the celestials and the sages. A chorus of voices from the heaven said, “You are Bhishma (the terrible – one who performed a great feat).” Satyavathi’s father accepted the marriage proposal and told Bhishma “I bestow my daughter to your father.”
Bhishma told Satyavati, “Oh mother, please get into the chariot and let us go to our house.”
After reaching Hastinapura, Bhishma narrated the events to his father . Hearing this, those assembled in the palace exclaimed, “He is really Bhishma.”
Santanu was overwhelmed by the sacrifice of his son for the sake of his happiness and gave him a boon that Bhishma would live as long as he wished to. “Death will approach you only after obtaining your command,” he said.(Bhishma made use of this boon by postponing his death till an auspicious time arrived after he was pierced by Arjuna’s arrows in the war.)
Prince Devavrata thus transformed himself into Bhishma, a man of sacrifice who would devote his entire life to safeguard the rulers of Hatinapura.