Billy Costigan Billy Costigan Jr. (Leonardo DiCaprio) is theundercover gangster for the Special InvestigationsUnit led by Captain Queenan. He is given the task of infiltrating the mob led by Frank Costello. He gets shot while attempting to take Staff Sgt. Sullivan into custody.
Collin Sullivan (Matt Damon) was introduced to the life of crimeby Frank Costello. Sullivan works with the Special InvestigationsUnit, trying to remain undercover for the mob. He dies at the end when Sgt. Dignam shoots him in the head (the two never got along in the movie)
Frank Costello (Jack Nicholson) is an Irish-American Mobster in Boston. He raises Colin Sullivan to become a mole in the Massachusetts StatePolice. Sullivan shoots Costello to his death during an altercation with the mob and police force.
Dr. Madolyn Madden (Vera Farmiga) plays the role of the moll. She builds intimate relationships with both Billy and Colin. Once Billy exposes Colin’ssecret to Madolyn, she leaves Colin. After Billy’s death, she left Colin for good.
Don’t have an ego! As in all good gangster films, the characters’ downfall was because of his ego.