Who is Marquis Urbain de Bellegarde from The American and what is their importance?

Marquis Urbain de Bellegarde is Valentin and Claire's brother. When Newman was in Urbain's presence, he felt as if he were in the presence of evil. During the party given for Claire and Newman by the Bellegardes, Newman notices that Urbain doesn't look pleased. When their engagement is later broken, Urbain frankly tells Newman that he does not and never did like him.