Vidura, the wise and intelligent step brother of Dhritarashtra and Pandu, was born to a Sudra woman, princess Ambika’s maid. Ambika was so terrified of Vyasa maharishi’s appearance that she sent her maid in her place and Vyasa impregnated her instead.

 
But this was not all an accident. Vidura, this son born of Vyasa, was Yamadharmaraja reborn on Bhumi owing to a curse. The curse was given to Yama by Sage Mandavya and it happened thus:
Mandavaya was observing a mouna vrat for years on end. He sat outside his hermitage though this period, eyes closed and hands raised in deep dhyana.  One day, some robbers came that way, fleeing with the stolen goods. The king’s soldiers were chasing them and were close behind. Terrified of being caught with the goods, they quickly hid it and themselves in Mandavya’s ashram.

 
The soldiers soon came there and questioned Mandavaya but restrained by his moun vrat, the sage did not answer. The furious soldiers searched the place and found the loot and the robbers. Assuming that the sage had been helping the wrongdoers, they arrested him too and presented him as one of the thieves to the king.  Unthinking, the king too sentenced the sage to a horrible death along with the robbers. He was impaled upon a sharp and long stake.

 
Then, a miracle occurred! Though impaled and left to die without food or water, the sage lived! Many rishis came to see him and shocked with his fate, they rebuked the king and told him who Mandaya was. The terrified king immediately had his men take the sage down and cut off the portion of the stake that remained outside his body. He then came to the impaled sage and begged forgiveness.

 
Mandavya continued his austerities with the stake embedded in him, earning the name Ani- Mandavya. While he had already forgiven the poor king, Mandavya had a niggling question in his mind about why he had been destined for such torment.

 
Mandavya went up to the region of the Gods. There he saw Yamadharmaraja and questioned him about why he was subjected to this kind of torture. Yama reminded him of an incident in the sage’s childhood when an insect had been impaled by him on a blade of grass.

 
Mandavya was furious. He berated Yama for giving him punishment that was not at all proportionate to the mistake committed, that too by a child. For this disproportionate punishment, Mandavya cursed Yama to be born as a mortal from a Sudra woman.  

So, Vidura was Yamaraja reborn and Yudishtira was born with the blessings of Yama as well. Several years after the Kurukshetra war, when Dhritarasthra left Hastinapur to go to the forest, Vidura went with him. The Pandavas went to see them there after a while and at this time, Vidura left his mortal body and his spirit entered Yudishtira.