Charlie was a “child” convict – around 15 years of age when he was transported on the second fleet. He has lived in Sydney Town since arriving in the open prison system, surviving more on his wits than anything else. Born in London, his Father was a drunkard who drove the family to a sentence in the local workhouse. Once the family debts had been repaid his Father deserted and Charlie was sent by his Mother to live with his Uncle and Aunt in Teddington. They were cruel and treated him like a slave. He ran away and became a member of a pickpocket gang. Charlie was caught, arrested, tried and subsequently sentenced to be transported for life.
Although he has been apprenticed to the local brickmaker, Charlie makes a profit from selling information. He is very short (given the poor diet of the age and the lateness people achieved puberty) and looks much younger than he actually is, allowing him to spy and largely be ignored. He speaks in a cockney accent. One of his best customers is the manservant of the Governor, who uses him as a line of information to keep the Governor informed of what is going on in the colony.
Although Charlie has limited literacy, he is naturally quite intelligent. He also has many useful skills such as lock-picking, pick-pocketing and others generally relating to larceny. He would certainly be someone the Doctor could rely on to pull through in a scrape due to his natural resourcefulness. While brave, he would tend to rely on cunning rather than brawn (partly due to his small stature) to survive in difficult circumstances.
By the time Charlie encounters the Doctor he is 19 or 20. I would envisage that the Doctor becomes a sort of surrogate father/teacher figure in his life. The Doctor might earn his respect by picking Charlie’s pocket at some stage. I think that he would have a natural aversion to authority and a distrust of any one who appears to be part of the ‘establishment’. The Doctor would be the perfect type of iconoclastic figure to be his mentor.