Hakuba Saguru was human - or at the very least, thought he was - until a Kid heist that ended badly. Since then, he's half human, half Time Lord, with a new (or old, it's only new if you've never seen it before) pocket watch with funny symbols both inside and out, and new (old) memories from his mother, who had run from the Time War and found 20th century Earth.
Due to the specifics of the bad heist, he also now has darker brown hair, deeper blue eyes, his skin's more tanned and he's ever so slightly shorter. He also has the Doctor's telephone number, having briefly met the man and his companion of the time, Donna Noble.
Please feel free to play anyone else from this 'verse if you've read the fic The Ticking Faces of Clocks. That's the only condition - that they're in character. Outside of Justonetruth I may use ideas that will be used in future installments set in his respective future, however.