Nephew was an Ood that lived with Auntie and Uncle on a asteroid - actually an accretion to a sentinent lifeform called House.
Biography
Nephew - like all there - was brought to House via a "sink hole" of the Universe, as the Doctor in his current 11th incarnation so ambigiously put it - "if it helps, it's not like that at all, but if it helps". There, he lived with Auntie, Uncle and Idris. He tended to Auntie's and Uncle's worries, similar to enslaved Ood. Soon after the Doctor, Amy and Rory arrived on the asteroid, Nephew became possessed by House and chased Amy and Rory through the TARDIS corridors. He eventually met his demise in the control room used by the Ninth and Tenth Doctors when the Doctor and Idris' makeshift TARDIS materialised in the space he was standing in. When he arrived, he came broken. The Doctor attempted to fix him, but it didn't last very long, and he only picked up Time Lord Hypercube transmissions, not the Ood's thoughts.
Powers and abilities
Nephew had the abilities of modified Ood, speaking using a translation sphere. He could remove the mind and soul of a person by placing his hands on their temples, leaving the body intact. This may have been due to House's influence.
Appearance
Nephew looked like all modified Ood, but had green eyes and a green translation sphere, possibly an effect of House's possession of him.