When Satyavati, a young beautiful girl was married to Shantanu, after his son Bhishma Pitamaha had renounced the right of succession and had tÃ¥ken the vow of perpetual celibacy. The sons of Satyavati had to succeed to the throne of Shantanu. Satyavati bore two sons; one of them died young in a battle. The other named Vichitra-virya ascended the throne. He also died young and without any issue. Before marrying Shantanu, Satyavati had borne Vyasa to the sage Parasara.
Thus Vichitra-virya, Bhishma and Vyasa were half-brothers, being the sons of the same father."With the consent of Bhishma and Satyavati, the widows of Vichitra-virya, Ambika and Ambalika by name, bore two sons through niyoga with Vyasa namely Dhritarashtra, the blind and Pandu with a pale complexion. Satyavati asked Vyasa to become the father of a third son, who should be without any defect. The widow of Vichitra-virya, terrified by the auster appearance of Vyasa, sent him one of her slave girls, dressed in her own clothes. This girl was the mother of Vidura.
Thus Dhritarashtra, Pandu and Vidura were half-brothers.Vidura was a great devotee of Krishna. In the first reference given above, Krishna addresses the king Duryodhana and shows his love for his devotee Vidura. Krishna stayed with his devotee. Vidura is one of the best characters in the Mahabharata. He always gave good advice to both Kauravas and Pandavas, though in the war, he sided with Kauravas. He was also a well-wisher of the Pandavas.
1. Kohli,Surindar Singh ed,Dictionary of Mythological References in Guru Granth Sahib 1993