In 'The Departed', which actor played Frank Costello?

In The Departed, Jack Nicholson played Frank Costello.

Costello is the film’s central criminal antagonist: an Irish-American crime boss operating in South Boston. He secretly places Colin Sullivan, played by Matt Damon, inside the Massachusetts State Police. At the same time, the police send undercover trooper Billy Costigan, played by Leonardo DiCaprio, into Costello’s organization.

Nicholson’s performance gives Costello an unpredictable, theatrical menace. The character is loosely inspired by real Boston crime figures, especially Whitey Bulger, although the film is not a direct biography. The Departed is primarily a remake of the 2002 Hong Kong crime thriller Infernal Affairs, relocated to Boston and reshaped by screenwriter William Monahan.

The role is sometimes confused with Robert De Niro because De Niro had a long association with Scorsese’s gangster films and was approached for another part in The Departed. De Niro did not play Costello; Nicholson took the role, while Mark Wahlberg, Martin Sheen, and Ray Winstone filled out the supporting cast.