Francis William Aston was among the most accomplished physicists of the 20th century. A Nobel laureate and Fellow of the Royal Society, his research career spanned four decades. During this time, he provided experimental proof for the existence of isotopes of many of the chemical elements and recorded their masses using several, hand-built mass spectrographs. A rather private man who lived alone in Trinity College for much of his adult life, Aston remains a somewhat elusive and mysterious figure. This biography attempts to shed some more light on the man, including his character and his personal life, and particularly how his life was shaped by his childhood, environment and education. It contains previously unpublished material and photographs and complements the biographies of Hevesy and Thomson, following Aston's death, and that by Squires detailing the construction and performance of his mass spectrographs at the Cavendish Laboratory. It is published at a timely juncture, some 100 years after Aston's first arrival at Cambridge.