General Sir Joseph David Frederick Mostyn KCB, CBE (28 November 1928 – 20 January 2007) was a British soldier and one-time Adjutant-General to the Forces.

Educated at Downside School[1] and at the Royal Military Academy, Sandhurst, David Mostyn was commissioned into the Oxfordshire and Buckinghamshire Light Infantry in 1949.

[2] He was mentioned in despatches for helping to suppress the Brunei Revolt in 1962 whilst serving with the 1st Green Jackets (43rd and 52nd).

[3] In 1969 he was appointed commanding officer of the 2nd Battalion The Royal Green Jackets and was deployed to BAOR and Northern Ireland.

[1] In 1980 he became Commandant of the British Sector in Berlin[1] and in 1983 he was appointed Military Secretary.