The Doctor (Alien Bodies)

The final incarnation of the Doctor died during the War; his corpse became the Relic. (PROSE: Alien Bodies)

Last adventures
Throughout the Doctor's adventures, he accumulated much knowledge and experience that was codified in his biodata, including the biodata codes of assorted Time Lord presidents. The Doctor's final incarnation claimed to the Celestis that he knew the codes used to build Mictlan and could destroy it at wish, though Trask believed he was bluffing. (PROSE: Alien Bodies)

Two days before the first battle of the War, one of the more interventionist and optimistic members of the Great Houses visited Dronid, claiming he had an old connection to one of the enemy's agents there. However, his diplomatic attempt apparently failed, and he was thought to have died as the battle started. (PROSE: The Book of the War)

However, Qixotl was involved in the true story of the Doctor's death, which was much more complicated. Even after the fighting on Dronid had already begun, a dying soldier was visited by the Doctor on Simia KK98; at that time, the Doctor said that he was just observing the conflict, that he wasn't working for the High Council, and that he was only one of the enemy "depend[ing on] where you stand." (PROSE: Alien Bodies) When asked who the enemy was, Abschrift replied, "Who indeed." (PROSE: Warlords of Utopia)

Right before the Cataclysm, the TARDIS materialised in the Grand Hall of Mictlan. The last incarnation of the Doctor told the Celestis that he wouldn't let them involve themselves in the affairs on Dronid, and they agreed to remain neutral if he gave them his corpse. He accepted these terms, but only if they freed some of their servants and satisfied one other stipulation.

After being captured into Marie's interior dimensions, the Eighth Doctor had a premonition of his future self's confrontation with the Celestis. During the premonition, he said that he had been a slave; the Eighth Doctor wasn't sure why he said this. (PROSE: Alien Bodies)

After death
After eventually dying, the Doctor's corpse became known as "the Relic" and was planted in a bunker under the ruins of the city centre of Smithmanstown on Dronid. Since much of the information in the Doctor's biodata had been lost during the War, his body was very valuable to many Wartime powers, including the Time Lords, their enemy, Faction Paradox, the Celestis, UNISYC, the Daleks, and the Krotons. Since most psychics retained some power even after death, proportional to their powers while alive, the Relic generated a psychic "call" particularly attuned to nearby humans.

The Relic was eventually found in Smithmanstown by the Corporation. Sharp-toothed Celestis agents worked with Little Brother Kolman to steal it for Faction Paradox, but Cousin Sanjira didn't recognise its importance and instructed Little Sister Justine to dematerialise it.

From there, it crashed onto Earth and was put in the Toy Store, which was pillaged when the Daleks invaded. By 2169, the Black Man had it in his store in London, though he sold it to Qixotl shortly before Homunculette came looking for it.

Qixotl set up an auction for the Relic on Earth in the late 21st century, creating the Unthinkable City to hold it. He invited only a select group of people interested in the Doctor's body for an actual purpose, rather than risking inviting those who just wanted to mutilate it for revenge against him. The auction did not go to plan, due to such factors as the Krotons taking the place of the Daleks and the inherent danger of the various powers bidding for the Relic.

The Eighth Doctor arrived after hearing news of the auction and soon determined what the Relic actually was, even if he avoided learning any specific details about where or how he would die in the future. During the subsequent crisis, at one point the Doctor managed to link with the Relic's psychic energy to expel a Faction Paradox agent that had possessed one of the human delegates. The Doctor tried the Celestis into thinking that they had "marked" him as their agent in this body, rather than immediately prior to his death, making the Relic into a temporal paradox; in reality, they had marked Mr Shift. The Doctor was free to leave with the Relic, which he took to the planet Quiescia and destroyed with a thermosystron bomb. (PROSE: Alien Bodies)

Description
After his death, the Doctor was stored in a metal box with the Greek letters "Theta" and "Sigma" on it. (PROSE: Alien Bodies)

Behind the scenes

 * PROSE: The Book of the War states that this future Doctor is a diplomat on the Homeworld. Given the suggestions in that story and PROSE: The Taking of Planet 5 that the War King is the Magistrate from PROSE: The Infinity Doctors, this lines up with the idea that this Doctor is the incarnation from the Infinity Doctors universe.