Vidura (विदुरः)

After going about in the world for many years with the tip of the trident in his body, Ani Mandavya once asked Dharma : "Oh! Lord, why is it that an innocent man like me is afflicted with the trident ?". Dharma answered: "In your boyhood you once caught small birds and pierced them with a grass reed. It is a result of that sin that you have been pierced with the trident." Mandavya replied : "The Sastras ordain that there shall be no punishment for sins committed till the age of twelve. Therefore the punishment inflicted on me is wrong. As the murder of a Brahmin is a greater sin than any other murder, may you be born as a man in the 'Sudra Caste'." By the above curse of Mandavya, Dharma was born a son of a Sudra woman. It was this child who later on became the renowned Vidura of the Mahabharata. (M.B., Adi Parva, Chapter 107).

Yama was once cursed by the sage Ani Mandavya. It was as a result of it that Yama was born as Vidura. (Page 367, Puranic Encyclopedia - Vettam Maṇi)