Idris

Idris was a human who's body was used as a host for the Doctor's TARDIS.

Biography
Idris found herself on House when a temporal rift transported her there. On the asteroid, she lived with fellow humans Uncle and Auntie and an Ood called Nephew. Unlike her fellow humans, she was never 'repaired' by House. Nephew (under House's orders) later drained Idris of her mind and soul in preparation for the arrival of a Time Lord, the Doctor. House then removed the matrix from the Doctor's TARDIS and contained it inside Idris' body. At this point, though her body was still intact, Idris essentially died.

As the TARDIS
When the Doctor, along with Amy Pond and Rory Williams, arrived on the planet, they were spotted by Idris, who now housed the soul of the Doctor's TARDIS. She started kissing the Doctor, calling him 'her thief', and speaking in strange ways, being unused to talking. She told the Doctor that 'the little boxes [would make him] angry'. When told to get some rest Idris asked if there was an off switch and instantly fell asleep, before being carried away by Nephew. She was locked away in a small cell and began saying random phrases without knowing why. She wondered where her thief was and called loudly for him.

When the Doctor found her, she explained that she was the TARDIS after making her engine sound. She began predicting what he would say, while she herself said some of the phrases she had mentioned earlier due to the TARDIS's non-linear perception of Time. The Doctor let her out, and the pair watched Auntie and Uncle die. When the Doctor asked her if she had a name of her own, she responded that the Doctor had given her the name "Sexy" when in private, embarassing him a bit. Idris realised that her body was too weak, and she had under an hour left to live.

Eventually they agreed to rebuild a TARDIS console from all the junk, while they bonded. Idris seemed disturbed by so many dead TARDISes, and told the the Doctor that while she never took him where he wanted to go, she always took him where he needed to go. She also revealed that she wanted to escape from Gallifrey and see the universe, so she "stole" the only Time Lord mad enough to travel with her, instead of the Doctor taking her just because she was unlocked. Idris infused the mechanical bits with a part of the TARDIS' inherent energy to allow them to follow House.

The Doctor had Idris send a telepathic message to Amy with details on how to get to a backup control-room and raise the shield; having been told by the Doctor to send a message to 'the pretty one', Idris sent the message to Rory.

When they got the shield down, the new console landed on Nephew, blasting him into atoms. The Doctor quickly introduced Amy and Rory to Idris, who introduced herself as 'Sexy'. Idris collapsed, close to the end of her life. The Doctor tricked House into transporting them into the main control room. The Doctor pretended to congratulate House for defeating them, while Idris, about to die, whispered "the only water in the forest is the river" into Rory's ear. The matrix was released inside the control room and merged back with the TARDIS. It proceeded to purge House from the TARDIS in a battle of souls that House couldn't win. With the last of her energy, the matrix used Idris's body to tell the Doctor that, although she would always be there for him, this was the only occasion when they could talk, using her last moments with a voice to say the word she never got to say to him when he first left Gallifrey: "Hello. Hello, Doctor. It's so very, very nice to meet you." (DW: The Doctor's Wife).