( The BH in this name is pronounced like a hardened sound of 'b' in 'beep'. The SH is pronounced like 'sh' in 'wish'. In the alternative name, the D is pronounced like 'th' in 'they'. The TH is pronounced like 'th' in 'with'.)
Bheeshma was the son of Shanthanu and the river goddess Ganga. He was manifestation of the eighth Vasu ( Prabhaasa) of the Gods. His original name was Devavratha. He is variously referred to as Bheeshma, Devavratha, Gaangeya, Shaanthanava, River's son, Pithaamaha (grandsire) etc.
After some years, Shanthanu wanted to marry another girl Sathyavathi whose father Daasha accepted the proposal only subject to the condition that her own son should ascend the throne after Shanthanu. Obviously, Shanthanu was against that condition , unwilling to detriment Devavratha's rights and interests . Devavratha learnt that and assured Daasha of what he desired. But Daasha expressed doubt about the possibility of Devavratha's sons coming in the way in future. To obviate such possibility, Devavratha declared that he would remain celibate forever. That great vow made the gods hail him as Bheeshma (= the tremendous). Since then he was more known by that name. Shanthanu got pleased with his son's pious deed and awarded him a boon that he could die only at his will.
He was respectfully called the grandsire by all. He truly stood by his words and never staked a claim to the throne even when there was an urge from his mother in a no-other-go situation too. He acted as an ideal trustee to the throne till his death.
In the Mahaabhaaratham war, Bheeshma was first made the army chief of Kouravas. Yudhishthira dreaded the grandsire very much . Minutes before the war, he went to the grand old man to bow and seek his blessings for victory . He even prayed to tell them the way to win him . Bheeshma, however, blessed and told him to visit again for that purpose .Bheeshma was not to be killed by any one unless he decided himself to die. Also, he set a rule for himself not to shoot at women, woman-turned-man, childless, brotherless etc. With these stringent conditions, he lead his side in the war for ten days killing ten thousand warriors a day . No one could stand against him in the war including Arjuna, despite Krishna's relentless encouragement. Bheeshma's invinciblity irritated Krishna himself and he took up his disc to kill Bheeshma, but Arjuna stopped him with great difficulty. This happened twice , once on the third day and again on the ninth day . The Paandavas and Krishna approached him late in the night of the ninth day and urged him to reveal the way to kill him . The brave grandsire explained to them that he would not fight with a woman-turned man . They took the hint and brought Shikhandi to Bheeshma's front in the following day's war. Shikhandi was none other than Amba , who took birth as a woman but turned into a man with the cooperation of a Yaksha in an unusual situation . Finally Bheeshma fell to the powerful arrows of Arjuna who took guard behind Shikhandi. But he remained alive on the arrow bed for nearly two months and finally died at his will in an auspicious period (i.e Uththaraayana, when the sun enters the zodiac of Capricorn) that he looked for.
Though young, valourous and powerful , he was never unruly. He took a firm stand to remain bachelor for ever for his father's cause and he swerved not . Also, he was committed to the word given to Daasha and never entertained the thoughts of staking a claim to the throne even on being urged by his step mother Sathyavathy herself . He acted as an ideal trustee to the throne till his death.
He understood that the incorrigible Kouravas were jealous and always condemned their crooked ways . He prevailed upon Dhiratharaashtra to disown Duryodhana for the good of the clan and land but his word went into deaf ears.
Many critics find fault with him for his scilence in the ugly scene of disrobing of Droupadi by the Kouravas right before his eyes . That sounds reasonable , but we should understand that he was committed to guard the throne and the king ,yet he had no vested powers to order any ruling king . His sticking on to the Kouravas side must be understood as his faithfulness to the throne but not to his unruly grandsons. The revealing of his death secret to the Paandavas was also considered immoral by some critics. But, it was about his own life that he risked , not the lives of others. Or, he might have thought that allowing victory to either side made no difference to him .
Anyway, no person can satisfy the world by all means. With his seeming tilt towards the Paandavas,whom he believed were righteous, he was to bear the public opinion that he was biased in favour of the Paandavas . Leaving those minor aspects that our current day assessment disapproves, he was no doubt an ideal character by any standards . Even today, the Indians pay tributes to him by respectfully offering propitiating ritual waters in commemoration of his death i.e. on the eleventh day of the month of Maagha, roughly corresponding to mid-February, every year. The five days of the month of Maagha from the bright seventh to the bright eleventh day are known as Bheesma-Panchkam i.e. Bheeshma's five days. Popular belief was that Bheeshma passed away on the elevennth day, but scholars maintain that he passed away on the seventh day .
It was said that even the illiterate Akbar had commented after hearing the Mahaabhaaratham :
"One old man and one young man I like." [ Ek boodha our ek ladaka
He was referring to Bheeshma and Abhimanyu seperated by four generations.