Compassion

Compassion was a remembrance of a Human who joined the Remote. She traveled with the Doctor, during which time she evolved into a TARDIS.

Biography
Compassion was originally Laura Tobin, a woman residing on the original colony of the planet Anathema. She, like all the colony residents, either was or became sterile. They thereafter reproduced using Remembrance Tanks, and over the millennia that the ship that Anathema was based upon took to get to Earth, all the colonists were "remembered" using biomass inside the remembrance tanks. Compassion is the result of this process.

Compassion was a member of the Remote, an offshoot of Faction Paradox. Following her encounter with the Doctor on Earth she chose to travel with him and Fitz (whom she, as Laura Tobin once knew). She also knew Kode, who was the remembered version of Fitz). (EDA: Interference - Book Two)

As Compassion came from a media/signal orientated culture she always wore an ear piece (or receiver). In an attempt to protect her from any 'harmful' signals she might encounter during their travels, the Doctor interfaced her receiver with the TARDIS systems. This interface had unforeseen results, warping her biodata along Block Transfer Computations, culminating in her 'birth' as a sentient TARDIS.

With his own TARDIS having been apparently destroyed in a dimensional rift, and the Time Lords now seeking Compassion to use her as breeding stock to create their own sentient TARDISes, the Doctor and Fitz were forced to use Compassion to go on the run. (EDA: The Shadows of Avalon)

Eventually, however, they were drawn to Gallifrey by the presence of the Edifice just before the Faction Paradox attack and Gallifrey's eventual destruction. After the destruction of Gallifrey, Compassion took the Doctor and the TARDIS- now totally drained of all its energy- to 19th century Earth, subsequently taking Fitz Kreiner to 2001 so that he could meet the Doctor after the TARDIS had repaired itself, and left to explore the Universe with a Gallifreyan technician, Nivet. (EDA: The Ancestor Cell, Escape Velocity).

Second War in Heaven
In a timeline where the events of the Second War in Heaven were not erased, Compassion was involved to some degree in the first battle on Dronid.

At a later point Compassion met Carmen Yeh in 1758, who began to travel with her. During this time, Compassion came to an agreement with the War King to create a "second wave" for the war. Compassion also warned the War King that House Lucia was a large event in the near future for him, but did not elaborate on what she meant. (FP: The Book of the War)

Compassion was later contacted by the embodiment of human technology. They made a deal that resulted in the creation of the City of the Saved. The City itself was Compassion who fired herself at the barriers between her universe and the next, Compassion was still connected to the universe via the Uptime Gate. (FP: Of the City of the Saved...) Grandfather Halfling was an old friend of Compassions who was present at the creation of the City and helped Compassion somewhat in creating it. (FP: The Book of the War)

Appearance
Compassion had coppery-red hair and freckles however once she became a TARDIS, her appearance was more a matter of her whims at the time, her freckles were described as being "far too symmetrical to be natural". (FP: Warring States) The Doctor and Fitz later referred to a time when they travelled the universe in a stroppy redhead. (EDA: EarthWorld)

Abilities
Once she became a TARDIS, Compassion's senses extended into other dimensions. She could generate a force field around her and could deliver painful electric shocks if attacked. She once accidentally overloaded the brains of four humans by attempting to contact them via her telepathic circuits, temporarily disorientating them. (EDA: The Space Age)

As a TARDIS, Compassion's internal dimensions were mapped to her psychology, full of twisted forests, and dark echoing spaces that she forced the Doctor and Fitz to inhabit. Her console was a black version of the one in the TARDIS she was familiar with but with a crystal spire in the center of it,. The controls constantly moved based upon how helpful Compassion felt towards the Doctor at the moment. Compassion used her newly found psychic abilities to influence Fitz's dreams; he admitted to suffering from nightmares when they travelled together, until Fitz and Compassion reached an understanding. (EDA: The Fall of Yquatine)

Behind the scenes

 * Compassion is one of the only ongoing characters from Doctor Who to also appear in the spin-off book series, Faction Paradox.
 * Physically, a fictionalised version of Compassion evidently resembled the actress Nicole Kidman. (EDA: Interference - Book Two). However, she was described as being "gerbil-faced and chubby". This description fluctuated throughout the series with Fitz thinking she's rather plain but with enough "curves" to make her appealing.