Bhishma was a great warrior and had great knowledge of politics apart from Krishna .He was able to challenge and defeat Parshuram who was his guru .He took the Bhishma pratigya of lifelong celibacy so that his father could marry the woman he loved .The father of the girl wanted that his daughters sons should get the throne and any rights associated with it .
Krishna and Pandavs had to use some clever manipulations and shikhandi as a shield to kill this great warrior . Eventhough he was stuck with a large number of arrows he continued living and died only when he felt his work was done .
