Figure of Speech
Antonomasia
From Greek antonomazein: to name instead. A classical device; common in epic epithets and later in everyday language where proper names become generic.
Definition
Substituting a proper name with a descriptive title, or using a proper name as a common noun.
Example
'The Bard' for Shakespeare; 'a Casanova' for any charming seducer; 'a Machiavelli' for a schemer.