Possible Clues:

• Villainous scientist character, say
• Typical Bond foe
• Superhero nemesis, often
• Villain who's both admired and feared
• Difficult-to-outsmart villain
• Supersmart supervillain
• Villainous scientist character, maybe
• Mad scientist, maybe
• One who might cackle 'Mwa-ha-ha-ha!'
• Enemy who's difficult to outsmart