Lt.-Col. Sir John Mansel Miller GCVO DSO MC (4 February 1919 – 17 May 2006) was a British Army officer and equestrian who served as Crown Equerry to Queen Elizabeth II from 1961–87.
Miller was born in Wheatley, Oxfordshire, the third son of Brigadier-General Alfred Douglas Miller and Ella Geraldine (née Fletcher). His mother was a descendant of political writer Andrew Fletcher, and of the Earls of Wemyss and March. His maternal great-grandfather Christopher Rice Mansel Talbot was Member of Parliament for Glamorgan for 60 years and Father of the House. His great-great grandfather was Richard Butler, 1st Earl of Glengall.
Miller grew up at the family estate of Shotover Park. He was educated at Eton College, followed by the Royal Military Academy Sandhurst.
In January 1939, Miller was commissioned into the Welsh Guards and served with the British Expeditionary Force after the outbreak of war. He was a courageous soldier who distinguished himself during the war, and was honoured for his bravery during and after the Allied Invasion of Normandy in 1944. He was awarded the Military Cross in December 1944, while serving as a major commanding the 1st Battalion Welsh Guards, with the citation noting, "that in the North Western Europe theatre of operations, after D-Day, in the face of heavy shelling, he kept his beleaguered men together, continually exposing himself to enemy fire, with complete disregard for his survival."