Johnny English/WMG

Bough is the real secret agent. Johnny English is just his cover or sidekick.
Their personalities just make it LOOK like Johnny is the secret agent.

Bough is rather quiet and appears to be shy, whereas Johnny English is brash, idiotic and VERY outgoing. But Bough is the one who is an official agent. Johnny simply has a desk job until his "promotion". Johnny runs around causing chaos, harassing Sauvage, and generally trying to be the secret agent; Bough runs around behind the scenes getting the needed evidence and bailing Johnny out when necessary.

Hey, most good spies are quiet and reserved. That way, they can get away with more before the other side catches on.