The Thomas Jefferson Building, also known as the Main Library, is the oldest of the Library of Congress buildings in Washington, D.C. Built between 1890 and 1897, it was initially known as the Library of Congress Building. In 1980, the building was named in honor of Thomas Jefferson (1743–1826), a Founding Father, the principal author of the Declaration of Independence, and the third U.S. president. In 1815, the purchase of Jefferson's book collection formed a core foundation for the library's collection.