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. He 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 over time, 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.
It was also during this time that the Doctor first met what would become his most persistent adversaries — the Daleks and the Cybermen. It would be the latter encounter that would see the Doctor first regenerate; stating "This old body of mine's wearing a bit thin," he collapsed at the end of the serial, regenerating inside the TARDIS into the Second Doctor.
William Hartnell described the Doctor as "a wizard", and "a cross between the Wizard of Oz and Father Christmas". One quirk of the First Doctor was his tendency to become occasionally tongue-tied and stumble over words. Sometimes this was a deliberate acting choice: William Russell recalls that it was Hartnell's idea for the Doctor to get Ian Chesterton's surname wrong, calling him "Chesserman" or "Chatterton". This character choice also gave the series' producers the ability to use takes in which Hartnell flubbed his lines. Due to the series' tight production schedule, it was rarely possible to reshoot such scenes and dubbing the dialogue was usually not an option. Hartnell suffered from undiagnosed arteriosclerosis, which affected his ability to remember lines, increasingly so as his time on the series progressed.
In the original pilot, the Doctor wore a tie and relatively contemporary clothes (below). When the pilot was reshot, however, his costume changed to a more Edwardian ensemble.Babelcolour Tribute
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