Leonardo is a short, mostly bald man with pale skin who wears round glasses. His head is football shaped with a large round nose and dark hair just around his ears. Like Clyde, he wears a white body length, long-sleeved lab coat and black shoes.
Leonardo doesn't speak; he only whispers to Clyde to inform him of his ideas. Leonardo frequently invents or perfects an invention, but Clyde takes the credit from him. Leonardo's usually emotionally displeased when Clyde insults his intelligence.