William Hartnell

From the beginning, the First Doctor was a mysterious figure. He appeared to be a frail old man, despite the eventual revelation that he was actually the youngest of the Doctor's incarnations, and yet was possessed of unexpected reserves of strength and will. (An early writers' guide by script editor David Whitaker describes "Doctor Who" [sic] as "frail-looking but wiry and tough as an old turkey".) He obviously held tremendous knowledge of scientific matters, and yet was unable to pilot his TARDIS time ship reliably; his granddaughter Susan explained this by saying that her grandfather was "a bit forgetful". He was abrasive, patronising, and cantankerous towards his human travelling companions, yet shared a deep emotional bond with his granddaughter Susan. He also harboured a streak of ruthlessness, being willing to lie and in one case attempt to kill to achieve his goals. Initially, he distrusted his first two human companions, Ian Chesterton and Barbara Wright, who were forced on him. Over time, however, as they shared adventures together, he grew closer to them, and the TARDIS crew came to share almost a family bond.

Eventually, the Doctor began to enjoy his travels through time and space, taking people along for the ride and was always reluctant and sad to see them go, even when he knew it was for their own good. The Doctor's personality mellowed around the time of the serial Marco Polo, and he evolved into the more familiar grandfatherly figure that children loved. Despite his age, the Doctor was never conservative, and was always a bit of an anti-establishment figure, opposing tyranny and overreaching authority in all its forms.

In the original pilot, the Doctor wore contemporary clothes (Including a suit and tie). When the pilot was reshot, however, his costume changed to a more Edwardian ensemble. The first incarnation of the Doctor carried a wooden walking cane, with a twisted handle. In one occasion, he was seen smoking a large bent tobacco pipe; to date, he is the only incarnation of the character to be seen smoking.