Who serves as the Captain General of the Royal Navy?

The role of Captain General of the Royal Navy is held by the reigning monarch, which is why King Charles III is the correct answer. This position symbolizes the sovereign's ceremonial relationship with the Royal Navy. The monarch's involvement with the navy serves to reinforce the connection between the armed forces and the nation, highlighting the importance of tradition and continuity within the military structure.

The other choices represent distinguished individuals within the Royal Navy and the armed forces, but they do not occupy the ceremonial role associated with the Captain General position. While Admiral Sir Ben Key, General Gwyn Jenkins, and Vice Admiral Martin Connell may hold significant ranks and responsibilities within their respective commands, they do not function as the head of the Royal Navy in the symbolic and ceremonial capacity that the monarch does.