Original Text Vidur Niti - Mahabharat - Udyog Parva (33-41) in Sanskrit

Vidura was half-brother of King Dhritaraashtra and Pandu.   

King Vichitraveerya had two wives, Ambika and Ambalika.  However before any child was concieved the king died due to a tragedy. Vichitravirya's mother, Satyavati, wanted the royal line to continue.  Ambika gave birth to Dhritaraashtra and Ambalika to Pandu fathered by Vyasa at the behest  of his mother Satyvati.   Vidura was born of a handmaiden of Ambika by Sage Vyasa.  He was therefore half-brother to both Dhritaraashtra and Pandu.

Vidura is the incarnation of Yama, the very embodiment of dharma.  He took birth as a human being owing to a curse by sage Mandavya.  Yama had imposed punishment far in excess of the sin committed by the sage unwittingly as a boy. Hence the curse on Yama.

Vidura was raised and educated by Bhishma along with his half-brothers. He was known for speaking the truth and for his intelligence and depth of knowledge. He served his brothers as a minister. He was a friend of the Pandavas and a great devotee of Krishna.  In spite of being a royal minister he led a simple life.

Vidura Neeti, mainly on the science of politics, is narrated in the form of a conversation between Vidura and King Dhritraashtra in the great epic Mahabharata.  It is often cited as the precursor of the more famous Chanakya Neeti.