He is Sir Richard Knighton, the Chief of the Air Staff (the only dedicated RAF 4-star post).
The rank was first used in 1922 when Sir Hugh Trenchard the then Chief of the Air Staff was promoted.
Up until the mid-1930s there was usually only one RAF officer in the rank of air chief marshal.
During World War II, with the great expansion of the RAF, the number of air chief marshals active at any one time peaked at nine during the War.
This number of air chief marshals was to remain approximately constant throughout the Cold War but after the British defence cuts of the mid-1990s there were only two dedicated 4-star RAF posts, namely the AOC-in-C, Strike Command and the Chief of the Air Staff.