The Great Bhishma
As already said, the king wanted to marry the daughter of fisherman - Satyavati. The father was accordingly informed. Here the fisherman became greedy! He thought, "As the tradition goes, Bhishma is elder and will succeed the throne of Hastinapur. My daughter's son will be younger and hence will be denied the chance to become the king. Moreover, when Bhishma marries, his son will succeed to the throne and not my daughter's son."
Hence, the greedy fisherman told her daughter to marry the king only on the condition that (1) Bhishma should never aspire for the throne of Hastinapur, and (2) secondly, he should never marry.
The two conditions were too harsh for king Shantanu to accept. This was clearly a great injustice towards his beloved son Bhishma. Therefore, the king did not accept the conditions immediately. He bought some time to give his final decision.
The days passed by. The king could not forget Satyavati, nor could he do injustice to Bhishma. This dilemma told on his health and performance of royal duties. He lost his appetite and took no interest in the affairs of his kingdom. These changes did not remain unknown to the intelligent eyes of Bhishma.
Bhishma decided to go to the root cause of the unhappiness of his father. He soon came to know all about his father's love for Satyavati and his desire to marry her. Bhishma decided to bring cheers in the life of his father. He went to Satyavati and, after introducing himself, requested her (would be step mother) to marry his father.
Satyavati repeated her two conditions to Bhishma now: that (1) Bhishma should never aspire for the throne of Hastinapur, and (2) secondly, he should never marry.
The firm-minded Bhishma vowed in front of her saying, "O mother, I, upon my word and in presence of this river Ganges, pledge never to marry and never to aspire for the throne of Hastinapur. In addition, till my last breath, I promise that I shall be loyal to the throne of Hastinapur whosoever occupies it." Thus indirectly Bhishma assured the fisher-woman that her son would be accepted as the future king of Hastinapur.
Happy days returned as the king Shantanu married Satyavati. The queen gave birth to two sons named Chitrangad and Vichitravirya.
The Kingdom Of Hastinapur
Days passed by. King Shantanu died natural death of old age. His elder son Chitrangad also died in young age. Hastinapur came under the rule of Vichitravirya and continued to flourish under his rule. Vichitravirya was married to three princesses, but as the fate had it, could not become father. Soon Vichitravirya also was killed in a battle without any issue. His queens were offered a child each from a great sage as a blessing and through his Yogic Power (without physical contact). The two queens followed the instructions and gave birth to Dhritarashtra and Pandu respectively; but the third queen sent her maid to the sage, and Vidura was born of the maid as the third son.
Dhritarashtra was blind from the birth, and therefore Pandu succeeded the throne of Hastinapur. Pandu, Dhritarashtra, and Bhishma grew up as friends and conducted the affairs of the state with great foresight. They all respected each other. Vidura was most righteous of all and was chosen as the Prime Minister of Hastinapur. Pandu married Kunti (aunt of Sri Krishna) and princess Madri; while Dhritarashtra was married to Gandhari, the princess of Gandhar. This noble lady also kept her eyes folded throughout her life as an mark of respect to her blind husband Dhritarashtra.