It began with the Daleks. Crude, and tired of life on their own deserted planet, they expanded outward. Planets fell to their unstoppable might, and entire stars collapsed, unable to hold against the dark. It fell to the Time Lords, self-proclaimed guardians of the cosmos, to stop the Daleks. The Time-Lords made great machines of war and destruction to halt the Dalek advance. Battles took place, stretching across planets and suns, time and space. The roar of a thousand TARDIS echoed through the years of the Time War, until finally the battle was brought to Galifrey, home of the Time Lords. In the final battle, neither side could achieve victory, for the risk of losing was too great, with the fate of all creation at stake. If the Time Lords fell, the final dam would break, and the Daleks would wreak havoc across eternity. And so the Time Lords, turning their great minds to a final solution, sought the exile. The one who would neither reap the benefits of victory, nor ever be able to ignore the cost. With his help, a final desperate strategy was formed, and above the skies of Galifrey, the Daleks and the Time Lords burned together. He had promised to fulfill that final duty to the end, and watch as the last of the Time Lords faded from existence, along with the threat that they had sworn to defend against. The Doctor watched it happen, made it happen, and when at last the cinders had lost all heat, and Galifrey collapsed into itself, he wept.
The Doctor returned to his own exile, never again to return to Galifrey. Galifrey had never existed, nor had the Daleks or the Time Lords. He was the last of a legend, whose source existed in whispers. In his travels, he found remnants of the great war. Fallen soldiers of the Daleks, turned to madness in the dark of their own minds. The Doctor found hope, in the form of an old Master, who had once sought to end all creation, but fled the Time War in fear of it. He too died in the end, despite the Doctor's wish that he should live. The Doctor found new companions, humans. Clever, unpredictable, and resourceful, he allowed a select few to travel with him. But, embittered by their mortality and fragile nature, he found himself unwilling to take them to places of real importance. They would fight no wars, the doctor abhorred violence. As much as he loathed Davros, he was right about certain aspects of his current incarnation.
The Doctor remained a lonely God, a testament to his own nature. He could travel through time, witness a supernova whenever he wished, however many times in a day he could manage, but still he traveled alone. His TARDIS grew to feel the same way, but had committed to helping the Doctor at the conclusion of the Bad Wolf scenario, where the machine had lent it's power to Rose, the Doctor's faithful companion, who loved the Doctor not unlike the TARDIS did. Rose had saved the Doctor's life, and understanding, the Doctor had returned the TARDIS' gift. In that moment, the two had shared an understanding, that they had one another's mutual support. The TARDIS would then take the Doctor to where beings suffered, and needed the Time Lord's help. He would be the Deus Ex Machina, the God from the Machine.
Oh, but how the worlds suffered.
This is the story of the man who gave himself to the universe, in the hopes of making a difference. The man who had everything to gain, and only his life to lose. A life he risked every day of his life to redeem himself for the monstrous act he committed, at the request of his own people.
And his song is ending.