This is one of at least two paintings of Sir John Mordaunt by Allan Ramsay, this one being exhibited in 1740. It hangs in Bodrhyddan Hall in Dyserth, Cornwall. Mordaunt was Colonel of 5 regiments in all, one of which he raised, the 47th Foot.
47th Regiment of Foot 15th Jan 1741 - 12th Mar 1743
He was also a Member of Parliament for nearly 40 years:
Regimental Details | Colonels