Nota Bene: I have tried to be as accurate as I can from the episodes that I have watched,
but quite a bit is of course pure speculation. The quotes are from Tennyson's Crossing the Bar which seemed beyond appropriate.
The Myth
"But such a tide as moving seems asleep,
Too full for sound and foam,
When that which drew from out the boundless deep
Turns again home"
When Theta was a boy there was a story, an old, old story about a man. A man of wealth and privilege, a lord who threw away his wealth and his titles to run away and see the stars. No one was quite sure what happened after that, some said he went mad from seeing so much of the creation, that all the pain and beauty and suffering and happiness destroyed what was left of the lord so that he was never the same again. Others said that he saw the stars and around them he saw life, beautiful, imperfect life and he gave away all that he had to heal and help wherever needed. That he could not walk by the suffering that he saw and so he spent his lives and loves helping anywhere and in any way that he could. Both stories agreed on only one thing, that he died and lived with loss and pain until he had no more to give. And then at the end, having seen planets born and galaxies fade away, with the light of the stars in his eyes and more knowledge than any other mortal he died for the last time, alone in all the universe.
Occasionally, in his more reflective moments Theta thought about the man in the story, the man without a name and wondered if it had been worth it, to give up so much and receive so little in return. Mostly though he would ignore it and think of something else, afraid of the sympathy that he had for the man in the myth.
Theta grew up though as all boys do and he thought less and less about the madman in the story and more on all the beautiful things he had in his life, his wife and children, grandchildren and friends that he had on Gallifrey. Indeed as the centuries slipped by he grew sedate forgetting his dream of running to see the stars. Almost he was content.
But the day came that his wife grew weak and ill and all the science of Gallifrey could not avail her. She died and Theta's hearts broke for the first time. And within his soul he began to remember his old desire to see the stars flick across the uncharted majesty of space. To see the wonders of creation in the light of a billion galaxies and the life that teemed, wonderful and varied across far flung planets and moons.
And the fire of adventure grew in his soul until one day he borrowed an old museum piece Tardis and ran away with his granddaughter to see the universe. He never thought of it at the time but the Timelord in the story had finally run away leaving behind his world. He stopped calling himself by his Gallifreyan name and began to call himself The Doctor, a man who healed, who rescued the oppressed and stopped children's tears.
His many Gallifreyan lives began to slip away, for the worlds he saved were not without their cost. Sometimes it was a life for a life, others a life for a hundred planets. But each was lived and each died in the end, killed as the madman spun his way through the stars. He took friends with him, gave them a glimpse of the wonders that lay beyond their worlds and taught them to be courageous and strong, to stand up and fight the good fight and if necessary to lay down their lives in its pursuit. And his loss became greater, his hearts breaking anew each time that he lost a friend or was unable to save or help someone. His own people were not sure what to do with him, sometimes punishing and sometimes honoring him. And he loved them all the same, despite their pompousness and arrogance and the hurt they inflicted.
The stories began to spread and he was given names by both friends and enemies. He was the Doctor by his own naming, choosing to forever heal rather than harm, to never give into to cruelty or cowardice, to fight through fear and pain and betrayal, to never give up and never give in. He was called the Oncoming Storm, Ka Faraq Gatri, the Last of the Time Lords, the Sainted Physician and the Lonely Angel.
But those who knew him best, who ran with him through the tangled beauty of space and time, they called him by the name that he had chosen for himself, The Doctor.
And when his time came at last, and he lay dying on the distant shores the unnamed sea in a remote and insignificant corner of creation he lifted his eyes to the stars one last time. His eyes that were old and young at once, that had seen so much of life and so much of death. His young body was slumped with the weight of millennia and the last wound of his life pouring away his life into the sand.
He thought of all that he had done in his time, both the good and the bad, his triumphs and mistakes and for the first and last time he saw himself clearly, without hate or arrogance and he was glad.
Because Theta knew that it was worth it and always had been.
"For tho' from out our bourne of Time and Place
The flood may bear me far,
I hope to see my Pilot face to face
When I have crost the bar."