William Chesterton

Major William "Bill" Chesterton was the paternal great-grandfather of the First Doctor's companion Ian Chesterton. His father was a drunkard and a gambler who habitually slept with prostitutes. He had an Aunt Mary.

Biography
In 1860, Major Chesterton was a member of the First Light Hussars of the British Army in Jaipur, India.

By 1865, he had been transferred to Guangzhou, China. During a mission to Qiang-Ling in that year, he fell off his horse and was concussed, losing his memories.

He bore a striking resemblance to his great-grandson, leading the First Doctor and Ian to mistakenly believe that he was actually Ian's future self who had been lost in time. This confusion was further aided due to Bill's partial-amnesia. It was finally established that the major's first name was Bill rather than Ian, after Captain Richard Logan corrected them on the matter. William Chesterton helped the Doctor, Wong Kei-Ying and others to defeat a resurrect Qin Shi Huang and the Mandragora Helix within him.

In 1890, Major Chesterton had retired from the army and translated the existing fragments of Mountains and Sunsets by Ho Lin Chung into English. (PROSE: The Eleventh Tiger)

Behind the scenes
The first name William is a reference to William Hartnell who played the First Doctor and William Russell who played Ian Chesterton.