Oval rooms became popular in eighteenth century neoclassical architecture, and it is likely that the architect of the White House, James Hoban, was influenced by the elliptical chamber of an Irish Mansion called Castle Coole. Here is a hand-tinted photo of the first Oval Office, designed by Nathan C. Wyeth for President William Howard Taft in 1909.
William Howard Taft’s Office in 1909 (White House Historical Association)
Warren G Harding ’s Office in 1923 (Library of Congress)
Calvin Coolidge’s Office in 1925
It can be said that from Howard Taft(1909) to Herbert Hoover(1933) the main decor of green rug, dark green drapes with eagle valances and olive green walls remained pretty much the same. When Franklin D. Roosevelt joined office in 1933, he redecorated it with a blue-green rug and gray green walls.
Replica of Franklin D. Roosevelt’s Office in 1933 (Roosevelt Library)
During Franklin Roosevelt’s Presidency, the office was moved to the southeast corner of the West Wing in 1934, and this is what the modern office looked like:
Franklin D. Roosevelt’s Office in 1936 (Wikipedia)
Harry S Truman in 1945 changed the tint of the room to grayish and his desk was famous for a plaque with a motto that read: “The buck stops here.”
Replica of Harry Truman’s Office in 1945 (Truman’s Library)
Dwight D. Eisenhower assumed office in 1953 and though he did not change the decor much…
Dwight Eisenhower’s Office in 1956 (EisenHower Library)
…he showed his taste in paintings.
The John F Kennedy’s Oval Office was redesigned by Stéphane Boudin in 1963 with a new red rug and pale curtains but it was dismantled after the President’s assassination, before Mrs. Kennedy returned.
John F Kennedy’s Office in 1963 (JFK Library)
Lyndon B. Johnson succeeded Kennedy and used his rug and curtains temporarily but he did not use the Resolute Desk.
Lyndon B. Johnson’s Office in 1963 (White House Historical Society)
He later changed the rug to gray.
Lyndon B. Johnson’s Office in 1968(Johnson Library)
President Richard Nixon started out with Johnson’s decor…
Richard Nixon’s Office in 1969 (NARA)
but he later changed to a Navy blue rug with gold drapes.
Richard Nixon’s Office in 1973 (NARA)
During Gerald Ford’s presidency which started in 1974 he opted for a pale gold rug with blue florettes and pumpkin drapes with gold curtains.
Replica of Gerald Ford’s Office in 1976 (Ford Library)
Jimmy Carter assumed office in 1977 but he carried through with Ford’s decor.
Jimmy Carter’s Office in 1976 (NARA)
Ronald Reagan too did not change the decor until during his second term when he opted for a pale gold rug with sunbeam design.
Replica of Ronald Reagan’s Office in 1979 (Reagan Library)
George H. W. Bush went back to the blue theme in 1989
George Bush’s Office in 1990 (NARA)
When Clinton came to power he changed to a colour scheme reminiscient of the Nixon era with navy blue rug and gold drapes.
Clinton’s Office in 1996 (Clinton Library)
Oval Office floor was replaced during the administration of George W. Bush. Based on a 1933 design by Eric Gugler, the 2005 installation is arranged in a contrasting cross pattern of quarter-sawn oak and walnut.
George Bush, Jr. revealed he delegated the decision of choosing the rug to Laura Bush, who chose a yellow sunbeam design. Here are a few snaps of Bush’s office:
George W Bush’s Office in 2005(White House)
So how is Obama’s office going to be? Any guesses? Are they discussing it? 
