Who is Tassoni from The Leopard and what is their importance?

Tassoni doesn't appear until the novel's final chapter, but he is spoken of much earlier - as a participant in a risqué story told by Tancredi.... a story that triggered the beginning of Tancredi's relationship with Angelica. During Tassoni's appearance, he reveals that Tancredi's story was a lie. Tassoni is a catalytic character, who serves to trigger transformation in others rather than undergoing any significant transformation himself.