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

Tancredi is the prince's nephew and ward. He is described as a handsome, sensual, free-spirited young man with a sharp wit, a powerful desire for women, and above all a driving, but lazy, ambition. His mother, sister, and father both died when he was young, leaving him in the care of the Prince, who is alternately exasperated and indulgent of his freewheeling, free-loving ways.