Related Clues:

• Clark Kent and Bruce Banner
• Clark Kent and Mr. Hyde, for two
• Many superheroes have them (2 words)
• Spaceman Spiff and Stupendous Man, for Calvin in 'Calvin and Hobbes'
• Secondary identities
• Cryptically goes for Batman and Robin, say
• Significant others? (2 words)
• Superheroes' secondary identities