Who is The Maestro from Heat: An Amateur's Adventures as Kitchen Slave, Line Cook, Pasta Maker, and Apprentice to a Dante-quoting Butcher in T and what is their importance?

The Maestro worked in Dario's shop when Bill apprenticed there. The Maestro taught Dario how to be a butcher and continued to work for him, cutting meat in his shop. Later the Maestro would teach Bill as well, teaching him how to butcher cows and pigs, a talent that Bill took home with him and practiced on a pig in his own home. Bill came to respect the Maestro a great deal and felt the feeling was mutual.