The Captain General Royal Marines is the ceremonial head of the Royal Marines. The uniform and insignia worn by the Captain General are those of a field marshal. This position is distinct from that of the Commandant General Royal Marines, the professional head (who is ranked as a major-general).
Captain General Royal Marines Wikipedia
The ceremonial head of the Royal Marines was the Colonel in Chief until the title changed to Captain General in 1948.
The post holders were as follows:King George V 1901–1936
King George VI 1936–1948
Colonel in Chief
Captain-GeneralKing George VI 1948–1952
Prince Philip, Duke of Edinburgh 1953–Present