A historian is a person who studies and writes about the past and is regarded as an authority on it. Historians are concerned with the continuous, methodical narrative and research of past events as relating to the human race; as well as the study of all history in time. If the individual is concerned with events preceding written history, the individual is a historian of prehistory. Although "historian" can be used to describe amateur and professional historians alike, it is reserved more recently for those who have acquired graduate degrees in the discipline. Some historians, though, are recognized by equivalent training and experience in the field. "Historian" became a professional occupation in the late nineteenth century at roughly the same time that physicians also set standards for whom could enter the field.

During the Irving v Penguin Books and Lipstadt trial it became evident that the court need to identify what was an "objective historian" in the same vein as the reasonable person, and reminiscent of the standard traditionally used in English law of "the man on the Clapham omnibus".

Robert Allan Caro (born October 30, 1935) is an American journalist and author known for his celebrated biographies of United States political figures Robert Moses and Lyndon B. Johnson.

After working for many years as a reporter, Caro wrote The Power Broker (1974), a biography of New York urban planner Robert Moses, which was chosen by the Modern Library as one of the hundred greatest nonfiction books of the twentieth century. He has since written four of a planned five volumes of The Years of Lyndon Johnson (1982, 1990, 2002, 2012), a biography of the former president.

For his biographies, he has won two Pulitzer Prizes in Biography, the National Book Award, the Francis Parkman Prize (awarded by the Society of American Historians to the book that "best exemplifies the union of the historian and the artist") two National Book Critics Circle Awards, the H.L. Mencken Award, the Carr P. Collins Award from the Texas Institute of Letters, and an Gold Medal in Biography from the American Academy of Art and Letters.

William Howard Taft (September 15, 1857 – March 8, 1930) was the 27th President of the United States (1909–1913) and later the tenth Chief Justice of the United States (1921–1930). He is the only person to have served in both of these two offices.

Before becoming President, Taft was selected to serve on the Ohio Superior Court in 1887. In 1890, Taft was appointed Solicitor General of the United States and in 1891 a judge on the United States Court of Appeals for the Sixth Circuit. In 1900, President William McKinley appointed Taft Governor-General of the Philippines. In 1904, President Theodore Roosevelt appointed Taft Secretary of War in an effort to groom Taft, then his close political ally, into his handpicked presidential successor. Taft assumed a prominent role in problem solving, assuming on some occasions the role of acting Secretary of State, while declining repeated offers from Roosevelt to serve on the Supreme Court.

Riding a wave of popular support for fellow Republican Roosevelt, Taft won an easy victory in his 1908 bid for the presidency.