Task: Question Answering
Input (English): Passage: Churchill's study, on the first floor, was his "workshop for over 40 years" and "the heart of Chartwell".
In the 1920s, as Chancellor of the Exchequer, he planned his budgets in the room; in the 1930s, in isolation, he composed his speeches that warned against the rise of Hitler and dictated the books and articles that paid the bills; in 1945, defeated, he retreated here to write his histories; and here, in final retirement, he passed much of his old age. Throughout the 1930s, the study was his base for the writing of many of his most successful books. His biography of his ancestor Marlborough and his The World Crisis were written there, and A History of the English-Speaking Peoples was begun and concluded there, although interrupted by the Second World War. He also wrote many of his pre-war speeches in the study, although the house was less used during the war itself. Tilden exposed the early roof beams by removing the late-Victorian ceiling and inserted a Tudor doorcase. From the beams hang three banners, Churchill's standards as Knight of the Garter and Lord Warden of the Cinque Ports and the Union Flag raised over Rome on the night of 5 June 1944, the first British flag to fly over a liberated capital. The latter was a gift from Lord Alexander of Tunis. The study also contains portraits of Churchill's parents, Lord Randolph Churchill and Lady Randolph Churchill, the latter by John Singer Sargent. The floor is covered with a Khorassan carpet, a 69th birthday gift to Churchill from the Shah of Iran at the Teheran Conference in 1943.Beyond the study are Churchill's bedroom and his ensuite bathroom, with sunken bath. At the time of the house's opening to the public in 1966, these rooms were not made accessible, at the request of Churchill's family but, shortly before her death in 2014, Churchill's daughter Mary gave permission for their opening, and the Trust plans to make them accessible by 2020. 
Question: What is the full name of the person that John Singer Sargent painted a portrait of?
Output (English): Lady Randolph Churchill.