Death (Timewyrm: Revelation)

Death was an Eternal and was one of the gods of Gallifrey. As such she represented and embodied Death itself.

Biography
Death was not the oldest of the gods; Pain was. But she was older than Time. (PROSE: Set Piece)

She came into being when Chris Cwej and Ishtar Hutchings had sex. Ishtar gave birth to Jasmine Surprise Cwej-Hutchings, who went on to have sex with Ricky McIlveen (a powerful psionic), who in turn gave birth to Death. (PROSE: Happy Endings)

There were legends that Death was apparently conceived when the "gods" were drunk. (PROSE: Return of the Living Dad) Being created from the dreams and thoughts of Time Lords, becoming personified into an "abstract universal entity." (PROSE: Human Nature)

Early in life, during the youth of his first incarnation, the Doctor killed Torvic. He made a deal with Death. Rather than having Death make him her champion, Death would choose another Time Lord, later known as the Master. However, the Doctor would later forget about this encounter. (AUDIO: Master)

The Doctor recalled seeing Death on a Gallifreyan hillside (presumably, before he knew who Death was). (PROSE: Set Piece)

The Seventh Doctor met Death for the first time on the Moon, when she was summoned by the Timewyrm as a robed skeleton. (PROSE: Timewyrm: Revelation)

Death briefly spoke to the Travellers in Puterspace stating that three quarters of them would die, but would not state which of them. (PROSE: Love and War, AUDIO: Love and War) The Doctor made another deal with Death to save Ace (presumably from the Hoothi) and offered himself in her place. (PROSE: Love and War) Death later took the life of Doctor John Smith. (PROSE: Human Nature)

On several occasions, the Doctor has said he was "friends" with Death. (AUDIO: The Death Collectors, Spider's Shadow)

Death picked Mortimus to be her champion, as a means of revenge upon the Doctor. (PROSE: No Future)

The Doctor once won a bet with Death. (PROSE: Sleepy)

Death, along with Time and Pain, attended Bernice Summerfield and Jason Kane's wedding in Cheldon Bonniface on 24 April 2010. (PROSE: Happy Endings)

When the Doctor suffered a one-sided heart attack at Roz Forrester's funeral, he had a vision of Death taunting him about taking the life of one of his companions, and that some day soon, she will take him, when he is alone and friendless, without warning and without meaning. (PROSE: So Vile a Sin)

Death appeared to the Doctor when he returned to the House of Lungbarrow. (PROSE: Lungbarrow)

At some point, the Doctor made a deal with Death, to give the Master a new start in life as a good and honest man for ten years, feeling guilty for how he turned out. However, after the ten years, it was agreed he would have to kill the Master.

When the ten years expired, Death sent the Doctor to Perfugium, where "John Smith" was living. Taking on the identity of John Smith's maid, Jade, Death tormented the Doctor, John Smith and his friends. This led to one of his friends, Victor Schaeffer, killing his own wife, and John's love, Jaqueline. When the Doctor couldn't go through with killing John, he realised his significance in creating the Master, and turned him into Death's Champion, by making his original deal with Death.

He constructed a new deal with Death, so that he wouldn't have had to kill John, but to kill an innocent person in the place of an assassin (who was just a disguise of Death again), but couldn't go through with that deal either. Death also made a deal with John Smith that to remain as John Smith, he had to decide whether he would make the Doctor Death's Champion, or if he would kill Victor so that Jacqueline would stay alive, but become the Master again. It is still unknown what his decision was. (AUDIO: Master)

The Doctor encountered Death again with Mortimus, which involved the Tramp. (PROSE: The Tramp's Story)

The Eighth Doctor knew the rituals involved in journeying to speak with Death. Sabbath followed the Doctor on his trip into Death's abode. (PROSE: Camera Obscura)