Richard Burdon Haldane, 1st Viscount Haldane, was a British lawyer and philosopher and an influential Liberal and later Labour politician. He was Secretary of State for War between 1905 and 1912 during which time the "Haldane Reforms" of the British Army were implemented. As an intellectual he was fascinated with German thought. That led to his role in seeking detente with Germany in 1912 in the Haldane Mission. The mission was a failure and tensions with Berlin forced London to work more closely with Paris.

The Secretary of State for War, commonly called War Secretary, was a secretary of state in the Government of the United Kingdom, which existed from 1794 to 1801 and from 1854 to 1964. The Secretary of State for War headed the War Office and was assisted by a Parliamentary Under-Secretary of State for War, a Parliamentary Private Secretary who was also a Member of Parliament (MP), and a Military Secretary, who was a general.