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.

In 1860, Major Chesterton was a member of the Hussar company of the British Army in Jaipur, India. By 1865, he had been transferred to China. He bore a striking resemblance to his great-grandson, leading Ian to mistakenly believe that his ancestor was his future self who had been lost in time. This confusion was further aided due to the major having suffered a recent head wound that left him with partial amnesia, until the TARDIS crew finally established that the major's first name was Bill rather than Ian.

By 1890, Major Chesterton had retired to his native England after many years in China and translated 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.