Possible Clues:

• Subject of Wagner songs perhaps quoted in Mastermind
• ...blame me for extra clause adopting unusual angle
• With injection of metallic element double the brains
• Instigator of illegal deals at auction
• Chief troublemaker
• One heading an illicit activity
• Glen raider going out as head of the gang
• One heading up illicit activity
• Instigator troubled grenadier travelling round lake
• Head of a cabal