Question: David Frederick Wallace was the brother of a First Lady who was married to which President?
Context: Frederick Wallace "Fred" Smith (born August 11, 1944) is the founder, chairman, president, and CEO of FedEx, originally known as Federal Express.  The company is headquartered in Memphis, Tennessee. First Lady of Chile (Spanish: "Primera Dama de Chile" ) is the unofficial title for the wife of the President of Chile, who is traditionally responsible for directing and coordinating activities in the social field of the presidency and also accompany the president in ceremonies or official activities, for example, on state visit.  In colonial times the wives of the Royal Governors were known as "Presidentas", title that was in use during the second half of the 19th century, but was slowly superseded by the newer of "First Lady".  Because this position is traditionally filled by the wife of the President, there is no clarity for the case of the spouse of a female president, regarding to the work that traditionally are performed by the first lady.  In these cases, the title "First Gentleman" ("Primer Caballero"; "Primer Damo", colloquially) has been proposed.  In March 2014, opposition newspaper La Segunda called Bachelet's son Sebastián Dávalos "primer damo". First Lady of Puerto Rico is the title given by the government of Puerto Rico to the spouse of the Governor of Puerto Rico or the daughters of the Governor should the Governor be a lady, single, divorced, or a widow.  The First Lady leads the Office of the First Lady of Puerto Rico and is expected to represent the women of Puerto Rico in elegance and demeanor.  The current First Lady is Beatriz Areizaga, wife of Ricardo Rosselló. David Frederick Schaeffer (born in Carlisle, Pennsylvania, 22 July 1787; died in Frederick, Maryland, 5 May 1837) was a Lutheran clergyman of the United States. David Frederick "Fred" Wallace (January 7, 1900 – September 30, 1957) was an architect and brother of First Lady of the United States Bess Truman. Sarah Angelica Singleton Van Buren (née Singleton; February 13, 1818 – December 29, 1877), was the daughter-in-law of the 8th United States President Martin Van Buren.  She was married to the President's son, Abraham Van Buren.  She assumed the post of First Lady because the president's wife, Hannah Van Buren, had died 17 years earlier and he remained unwed throughout the rest of his life.  Although she was never married to a president, she is the youngest woman ever to hold the title of First Lady. The Office of the First Lady of the United States is the staff accountable to the First Lady of the United States.  The office and its responsibilities, while not mandated, have grown as the role of the First Lady has grown and formalized through the history of the United States.  The Office of the First Lady is an entity of the White House Office, part of the Executive Office of the President. David Frederick (born April 9, 1961) is an appellate attorney in Washington, D.C., and is a partner with Kellogg, Hansen, Todd, Figel & Frederick, P.L.L.C. Elizabeth Virginia "Bess" Truman (born Wallace; February 13, 1885 – October 18, 1982) was the wife of U.S. President Harry S. Truman and First Lady of the United States from 1945 to 1953. The First Lady of the United States is the hostess of the White House.  The position is traditionally filled by the wife of the President of the United States, but, on occasion, the title has been applied to women who were not presidents’ wives, such as when the president was a bachelor or widower, or when the wife of the president was unable to fulfill the duties of the First Lady herself.  The First Lady is not an elected position; it carries no official duties and receives no salary.  Nonetheless, she attends many official ceremonies and functions of state either along with or in place of the president.  Traditionally, the First Lady does not hold outside employment while occupying the office.  She has her own staff, including the White House Social Secretary, the Chief of Staff, the Press Secretary, the Chief Floral Designer, and the Executive Chef.  The Office of the First Lady is also in charge of all social and ceremonial events of the White House, and is a branch of the Executive Office of the President.
Answer: Harry S. Truman