Steven
Out of all the people he had travelled with so far, he hadn't left any of them behind quite like Steven. His leaving had him puffed up proud as a peacock.
Steven left the TARDIS not on Earth, unlike any companion before him, but on a planet not of his own, in the far distant future, to look after and rule over a people alien to him.
He had been chosen as a leader, someone who could easily help and see the troubles of both the different factions on the world, and he had decided to stay behind and help them grow with one another, to bridge the enormous gap that had formed between the Savages and the ones who thought they were above all others.
For an advanced species, the Counsellors of the more advanced people surely were very closed minded. Still, with Steven's help, he was sure that everything would be well again with the civilisation. Sure that everything would get back on course soon afterwards.
He would be missed though, oh yes, missed very much, especially by dear Dodo, who had cried at his departure.
After Dodo had gone to her room for a bit of a rest, he had made his way back to the food and drink replicator and made sure he had a cup of tea ready in no time. He went off into the sitting room, to read some of the books that the civilisation as a whole had written.
While Steven was never mentioned, all was said was that a great leader rose up from the ruins and joined their peoples together. He had always thought of this book as one of the first, as there was no publication date. Now, he knew differently.
Chuckling, and having a sip of his tea, he toasted the empty air and smiled. "Good work, my boy. Very good work, indeed. I knew you were ready."
He spent the rest of the day reading quite happily.