Bhishma (भीष्म:) or Bheeshma, born as Devrata/Devavata, was the illustrious son of Goddess Maa Ganga and King Shantanu of Kuru Dynasty. He was the supreme commander of the Kaurava army in the Mahabharata war. Bhishma was the uncle of Dhritrashtra (धृतराष्ट्र), Pandu (पांडु) and Vidhur (विधुर), and the grand-uncle of Pandavas and Kauravas. Bhishma was considered a god-like figure with eminent warfare skills, a virtuous soul, a strong psyche, and a kind and noble heart. Bhishma was the elder half-brother of Vichitravirya (विचित्रवीर्य) and Chitrangada (चित्रांगद), who were the son of King Shantanu (शांतनु) with second wife Queen Satyavati (सत्यवती).
Bhishma was the heir-apparent of the Kuru kingdom and was even made the prince of the kingdom. However, he benevolently renounced the rights and took a lifelong vow/oath of celibacy or sexual abstinence (ब्रह्मचर्य). Because of this impulsive selfless fierce vow, his father gave him the name 'Bhishma'. King Shantanu also gave the boon of self-willed death (Swecchamritya or Icchamrityu; Self-willed death should not be confused with suicide.) to Bhishma. As per the boon, Bhishma could willingly choose the time, the way, the manner, and by the hands of whom to accept death from.
Other names of Bhishma
Bhishma was called Gangaputra ('the son of Ganga') in a matrilinear addressing style. He was given the title Mahamahim and was frequently called Mahamahim Bheeshma (महामहिम भीष्म:) by the people. Because of his white skin color and silver warrior attire, he was also called Gauranga (गौरंगा). The Kauravas and Pandavas called and addressed him as Pitamaha Bhishma or simply Pitamaha (Grand Father).
The matronymics of Bheeshma also included Gangasuta and Gangeya, while the patronymics include Shantanav, Shantanuputra, and Shantunuja.
In Hindu culture
Each year the death anniversary of Bhishma is celebrated as Bhishma Ashtami which falls in Magha (Jan-Feb) month of the Hindu calendar.