John Edward Bernard Seely, 1st Baron Mottistone,, also known as Jack Seely, was a British Army general and politician. He was a Conservative Member of Parliament (MP) from 1900 to 1904 and a Liberal MP from 1904 to 1922 and from 1923 to 1924. He was Secretary of State for War for the two years prior to the First World War, before being forced to resign as a result of the Curragh Incident. He led one of the last great cavalry charges in history at the Battle of Moreuil Wood on his war horse Warrior in March 1918. Seely was a great friend of Winston Churchill and the only former cabinet minister to go to the front in 1914 and still be there four years later.

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.