GANGAPUTRA ,"DEVAVRATA"
Devavrata or bheeshma was the son of king SHANTANU ( a ruler of the lunar dynasty) and Queen DEVI GANGA.
The Son was a prince , statesman , and military commander of the ancient kuru kingdom.
He was designated the heir apparent to the throne. However, he renounced his claim and took a vow of lifelong celibacy to facilitate his father's marriage to Satyavati.
This unparalleled sacrifice got him the name " BHISHMA", meaning " The one who undertakes sever vow".
Then also got a boon from his father of "Iccha Mrityu", meaning " The power to choose the time and manner to death".
[which later became a curse for him]
So, it was clear that Bhishma was indirectly immortal now and due to his vow of celibacy he had to serve his descendents for more than a century.
sources say that bhishma was 256 years old.
Apart from all those updates in his life.He was a man of his words.His Vow of serving hastinapur until his last breath made him fight against his loved ones.
He could not stop draupadi's disrob because of his lifelong vow to uphold the authority of the King, even if the King's actions were unjust.
Bheeshma has made a lot of mistakes just because he had taken some particular vow which did not allow him to do so. And, as he was a kshatriya he could not take his words back no matter the cost.
When draupadi arrived in hastinapur he was the most glorious one. He adored her like his own daughter. He only, claimed that draupadi is his favourite kulvadhu(daughter in-law) but then he had to see his favourite daughter in-law being pulled by her open hairs to a hall filled with courtiers.He had to see her clothes getting snatched by his own grandson(dushasan). He had to see his own descendents fight and the worst was that he had to fight among them.He had to regret the promises for which he sacrificed his whole life.At the time of his last breaths He regretted his mistakes,his vows,his every move that he did for his kingdom thinking it would cherish the future of his descendents and hastinapur.