Possible Clues:

• Witless one
• Trick officer, a fool
• Not the brightest bulb in the pack
• One who's slow on the uptake
• Point made about learner being an idiot
• Charlie had an impact after switching ends
• Brainiac's opposite
• Fool jolly officer
• Fool to impersonate an army officer
• Transient lodger accommodating fool going west