In 'The Departed', what is the name of the character played by Matt Damon?

In The Departed, Matt Damon plays Colin Sullivan, a Massachusetts State Police officer secretly working as an informant for mob boss Frank Costello.

Sullivan is one half of the film’s central undercover conflict. Costello recruits and grooms him from a young age, eventually placing him inside the police department. At the same time, the police send Billy Costigan, played by Leonardo DiCaprio, undercover inside Costello’s organization. Each side therefore has a mole searching for the other.

The film’s other major characters are easy to confuse with Sullivan. Billy Costigan is the undercover officer inside the mob, while Dignam is the volatile police sergeant played by Mark Wahlberg. Frank Costello, played by Jack Nicholson, is the Irish mob leader who controls Sullivan.

The Departed was released in 2006 and is a remake of the 2002 Hong Kong film Infernal Affairs. It was adapted for a Boston setting by screenwriter William Monahan. The film won four Oscars, including Best Picture and Martin Scorsese’s first Best Director award.