Devavrata in his previous birth was Dyu , one among eight vasus (a class of heavenly demigods ) who were cursed by great sage Vashistha to be born on earth as ordinary mortal . However , even curse of great brahmana like Vashistha , who is naturally kind to everyone , was a blessing in disguise and helped him to come out of enjoying mentality.
As a reaction of this curse , Devavrata was born from the womb of mother Ganga (whose origin is sacred feet of Lord Vishnu ) . Mother Ganga took his son Devavrata to heavenly planet for his initial education in the ashrama of sage Vashistha . Devavrata was equal to Brihaspathi himself in terms of knowledge of Vedas . Also in military science he was no less than great and powerful Parashurama.
Devvrata also took a life-long vow of celibacy and this was rare occurance among kshatriyas . Kshatriyas usually have many wives and sometimes hundreds of children . Because Kshatriya were in mode of passion (Refer Bhagwat-Gita As It Is, verse 14.12) this was almost impossible for them to control sex desire . They therefore took many wives and maintained them in great opulence . Thus, the name Bhishma was given to him , meaning one who has taken almost impossible vow to carry all trough his life.
By keeping the seminal fluid within, a man increases in strength , memory, intelligence, and duration of life . This was one reason why Bhishma was destined to become the most powerful of the great warrior.
Devavrata , because of his great devotion to the lotus feet of the Lord Krishna , was able to make a life-long celibacy vow , rejecting the feminine beauty of this world . Infact , he is one of the mahajana ( authority in science of devotional service to the lotus eyed lord Krishna ) . And when Bhishma was about to leave his mortal body , The Lotus Eyed Lord himself stood infront of him so that his mind can remain completely absorbed in him and he can return back home back to Godhead , the Spiritual World to lead a life of eternity , knowledge and bliss (Refer Bhagwat-Gita As It Is ,verse 8.5) .