In this alternate reality where my Doctor resides, instead of stealing a Type 40 TARDIS to explore the universe, He stole a TARDIS to run from the Time Lords after finding out of their corruption, in which they order his execution (because the Time Lords are corrupt and ruthless in this reality) and he hid on Earth, 1963 disguising his TARDIS as a Police Box.

Each day on Earth he would try to be human and socialize with the people on Earth.
Eventually he had forgotten about the Time Lords. He'd still check in on his TARDIS every now and then, seeing as she was the thing that brought him to safety so he thought he was repaying the favor. One day the Time Lords had finally found him. He wanted to run but something within him awoke, he felt courage and rage. And this time instead of running, he killed the Time Lords that were tracking him.

At the time he thought it was right,
but later on when he went back to his TARDIS, he realized what he had done and felt intense guilt and sadness. On that day he had promised himself "No killing." and "Never be cruel or cowardly." That was the day he became "The Doctor". Ever since, with his TARDIS he's been having amazing adventures that would further challenge his promises. When things were tough, he would think to himself "Just run!" but he never did. Instead of always running, he had saved millions of people because he never gave in to cowardice.

Then came the Time War, it turned out all the same as the main reality's Time War. He had turned into a man he refers to as "The Warrior" just this once. He had killed both of the Time Lords and the Daleks. After the Time War he had become the Doctor again, He felt it was his penance to keep on saving people across the galaxies. Time to time he would have a companion along with him to keep him in check. This skin is his most recent incarnation, his 12th.