The Relic was/would have been the body of the Doctor. It was contained in a metal box with the Greek letters "Theta" and "Sigma" on it, the box being launched through time using the Doctor's remaining psychic energy as a power source.
Had the War occurred and the Doctor progressed in his travels without the War encroaching on his past selves, he would have had many further adventures and accumulated a lot of knowledge and changes to his biodata prior to his death on the planet Dronid.
Much of the information stored in the Doctor's biodata was lost during the ensuing war, such as the various biodata codes of assorted Time Lord presidents. Thus, when he died his body became very valuable to:
- The Time Lords from the War's future, because of what it contained and what they had so far lost in the war.
- Faction Paradox, as due to their methods biodata would be very valuable to them, especially such a well-lived specimen as the (future) body of the Doctor.
- Other parties, including UNISYC, Daleks, Krotons, and the Celestis.
Even on its own, the Relic was unusually powerful; while most psychics retained some power even after death depending on their pre-existing power, the Doctor had such a significant psychic potential that the Relic was still generating a psychic "call" even after it was physically deceased, particularly attuned to humans in the vicinity.
After the battle on Dronid, the Doctor's body was apparently unearthed from the ruins, and sent into the Vortex by a Faction Paradox cultist who didn't realise its significance until it was too late. The Relic crashed on Earth in the early 21st century and was taken to the Store, a repository of alien technology kept by the American military. After the Dalek invasion of 2164, human military technology was scattered across the planet, allowing Mr Qixotl to recover the Relic and set up an auction for it.
Qixotl set up an auction for the Relic on Earth in the late 21st century, creating the Unthinkable City in which 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. Having tricked the various groups at the auction into thinking that the Relic was a temporal paradox by convincing the Celestis that they had "marked" him as their agent in this body rather than immediately prior to his death (in reality they had marked the conceptual entity known as the Shift that had been trapped in the Doctor's mind), the Doctor was able to leave with the Relic. He took it to the planet Quiescia and destroyed it. (PROSE: Alien Bodies)