Vidura
Vidura (Sanskrit: विदुर, lit. skilled, intelligent or wise) was the brother of Dhritarashtra and Pandu, and functioned as the main Counsellor to king Dhritarashtra. He was thus the uncle of the Pandavas and Kauravas.
Vidura was born from Niyoga- between sage Vyasa and Parishrami, a handmaiden to the queens- Ambika and Ambalika. Ambika and Ambalika were wives of king Vichitravirya - the grandfather to Kauravas and pandavas; and the father of Dhritarashtra and Pandu. Barring Krishna, Vidura was most respected as an adviser by the Pandavas, whom he forewarned on various occasions of Duryodhana's plots to exterminate them, such as Duryodhana's plan to burn them alive in the house of wax.
Except the prince Vikarna, Vidura was the only one who protested against the humiliation of Draupadi in the Kaurava court. In that moment, Duryodhana viciously rebuked Vidura, calling him ungrateful. Dhritarashtra moved to rebuke Duryodhana for insulting Duryodhana's uncle, but, remembering Vidura saying that a blind man cannot be king, holds his tongue, and instead reprimanded Duryodhana for insulting the prime minister. It is that incident that Vidura brought up years later when he severed ties with the Kurus and sided with the Pandavas at the onset of the Kurukshetra war. Unlike Bhishma, Drona, Kripa, Karna, etc., Vidura did not have an obligation to Hastinapur or Duryodhana, but to his family. Hearing Dhritarashtra not acknowledge that relationship, Vidura felt compelled to side with dharma and the Pandavas.
When Krishna visited Hastinapura as a peace emissary of the Pandavas, he shunned Duryodhana's offer to stay in the royal palace, preferring instead the home of Vidura, on account of him being the only neutral man in the Kaurava court. The reason Krishna stayed in Vidura's chambers for the night instead of Duryodhana's is due to the thoughts which were running through their heads and the difference between them. Duryodhana's intention was to heave luxury upon Krishna and convince him to join the Kaurava's side. Sensing this intention, Krishna refused. Krishna knew the food that Vidura presented was presented with love and affection with no ulterior motive.
In the Sanatsujatiya section of the Mahabharata, shortly before the Kurukshetra War began, Vidura invoked the sage Sanatsujata to answer Dhritarashtra's questions about death. In protest against the Kurukshetra War, Vidura resigned from the post of minister.