I am the Doctor

This particular version of the Doctor spent almost a year in a city ruled by beings claiming to be the Asgardian gods, brought there to fight a war in their name. When he, and every other being that was brought to the city, first arrived, they were rendered perfectly human and then given a power from their 'patron god'. His god was Baldr, and he was given the power of 'Regeneration' -- meaning, he can heal from most injuries within minutes. It does take his own energy to do this, and he doesn't do it automatically, so it's far from a perfect power... but it's far better than being a standard human, so he'll take it.

So many of his other selves also came to the city that they all ended up going by their numbers, other than his metacrisis self (Theta Sigma) and the War Doctor (I believe he decided to go by John). He will insist on going by some version of Six, or if that's not acceptable for some reason, 'Kitty'.

...don't ask.

Over the year he spent there, he saw his share of fighting and even killed people (under the influence of a corrupting force, but still). He died a few times as well, and learned things about his future he never wanted to know. He gained a girlfriend, and then a fiance when he proposed to her by mistake. He also got his second heart back, so he's got the cardiovascular system of a Time Lord while still being in all other respects very much a human. Mrs Faraday/The Widow may be helping him fix this particular problem, however.

The people he knows from Asgard include: Martha Jones, Jamie McCrimmon, Rose Tyler, Melanie Bush, Rory Williams, Amy Pond, River Song, Ianto Jones, Romana, Braxiatel, Clara Oswald, Remus Lupin, Ron Weasley, Jenny, Kate Stewart, Alice Liddell, Alan Walker, Charley Pollard, John Watson, King Arthur, Thor, Bruce Banner, Turlough, Jack Harkness

The Doctors that showed up in the game: 2nd, 4th, 8th, War Doctor, 9th, 10th, the metacrisis, and 11th