From bel canto brilliance to the earthiest chest tones, the mezzo-soprano has long been the unsung hero of the opera stage. Although they are often assigned the secondary role in an opera, make no mistake: These divas steal the scene whenever they are on stage. In this episode, Metropolitan Opera Radio commentator Ira Siff concludes his "Magical Mezzos" series some of opera’s most thrilling mezzo-sopranos, past and present!