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Billy's corpse.

William M. "Billy" Costigan Jr. was a police officer who infiltrates Frank Costello's crew and he is the main protagonist of The Departed.

He was portrayed by Leonardo DiCaprio.


Early life[]

Billy was born on November 7, 1984, to Catherine R. Costigan and William Costigan Sr., in Boston. He had relations with the Irish mafia in South Boston, from his father, who was not a gangster, but a baggage handler at Boston Logan Airport. He had relatives who were part of the Irish mafia, like his uncle Tommy Costigan who gets busted selling guns to federal officers, his cousin Sean Costigan, who is a drug dealer and best known of all, his uncle Jackie Costigan, respected by gangsters including Frank Costello himself. He also had relatives from his mother’s side on the North Shore (likely Andover), which appear as she is passing away from cancer in the hospital (Uncle Edward). His parents divorced from Billy's early age, forcing him to live with his mother in wealth on the North Shore, and on weekends in the Irish neighborhood of Southie. At some point in school he hit a sport teacher with a folding chair, in Deerfield. His father died at an unspecified point in the life of Costigan for unknown causes. Later his mother passed away as well, from an unknown sickness.

Police Academy[]

Billy decided to enroll at the Massachusetts State Police Academy shortly before his mother's death. Costigan begins in the Massachusetts State Police Academy, where he befriends Trooper Brown. Before he is able to graduate, he went to the Special Investigation Unit headquarters, where is called by Captain Oliver Queenan and Staff Sergeant Sean Dignam, and is brought into their office. As he begins his interview with Captain Queenan and Staff Sergeant Dignam. The two decide to put Costigan into an undercover operation in an attempt to infiltrate Frank Costello's crew, thanks to his contacts with the South Boston mafia. With a false accusation, he leaves the academy and serves time in jail and is placed on probation to gain credibility.

Release from prison[]

After Costigan left the police for four months[10], upon Costigan's release, he contacts his cousin Sean, and the two begin selling cocaine. In the evening with his cousin he goes to a bar in Costello in Worcester, where he beats a guy who made fun of him. He is stopped by Costello's right-hand man, Mr. French. The next morning in a bar, he beats two Italian-American mobsters from Providence. After these actions, on the evening of that day he met Frank Costello for the first time in a bar. As they goes to the backroom with Mr. French, French hits Costigan's injured arm onto a table and searches on him, saying he's clean. Frank then repeatedly hits Billy's broken hand, interrogating Billy with accusations of being a cop. Billy holds up under questioning. The next day Billy has an "interview" with Frank, and consequently joins Costello's crew.

Meeting with Madolyn[]

As part of his cover story as a disgraced policeman he must see a "court ordered" shrink. he has appointments with psychiatrist Madolyn Madden. However, he has a breakdown when is given only two pills and she orders him to leave. She meets with Billy outside to inform him that she will help him get over his distress, she then decides to transfer him to a different councillor and he asks her to meet for a cup of coffee, much to her surprise.

Finding Out Costello's Awareness[]

Costigan becomes aware that Costello is aware of having a rat in his crew. So, he calls for Queenan and Dignam. After briefly fighting Dignam since Dignam threatened to delete his file, he informs Queenan about Costello's awareness of the "rat" and will find out who he is. Dignam and Queenan reveal that Costello has a mole in the Special Investigation Unit.

The Deal[]

After a few months the Chinese arrive in Boston, while with Costello and his crew are in the Chinese deal, Costello is texted by Colin Sullivan to keep their phones off, in which Costello insists and tells his men to check their weapons and phones off. However, Costigan secretly haves his phone on and he slowly texts Queenan, informing him of the monies presence at the deal. As the Chinese leave with their microprocessors, Costello makes a remark, saying "They didn't figure we had a navy" to Costigan, referring to the fact that the Chinese are arrested, the microprocessors it turns out to be false. Later, he has a conversation with Dignam about Costello's awareness and Costello's mole in the SIU as he goes to meet with Madolyn.

Finding Costello's true agenda[]

Billy goes to a junkie's house as Mr. French sets off firecrackers to prevent schoolchildren and other civilians from hearing gunfire. He smashes a picture frame on the junkie's head, which wakes him up. He asks the junkie of what he does to pay. Soon, the junkie mentions Costello's involvement with the FBI. Costigan quizzes the junkie about the FBI, in which he profuses about being high, resulting in Costigan shooting the junkie in the kneecap. The junkie reveals that Costello is an FBI informant. Then, Costigan escapes with French. In the evening he goes to Queenan's house, Costigan informs Queenan that Costello is an undercover FBI informant and that he never gets busted since he is protected from his crimes. The next day, he picks up an envelope from Frank's crew hideout. He rewrites the word "cittizins" (Fitz misspelled it) to "citizens", in which Fitz believes it's wrong. He gives the envelope to Timothy Delahunt and leaves.


He meets Madolyn at her old apartment since she moved with Colin. She reveals that she moving with Colin to Costigan and soon after the two made love.

Tailing Colin[]

At a pornography theatre, Costigan spies on Colin, who is meeting with Costello. As he spies on them, Costello chats with Colin about Colin's "reassignment" and Costello gives him the "citizens" envelope. Then, when Colin leaves, Costigan tails him. Colin becomes aware and he sets out to hide somewhere to ambush him, in which Billy does the same thing. after accidentally murdering a Chinese Resturant worker, Colin successfully escapes. Colin goes to the SIU to see the camera footgram, and see Costigan's face, but he can't.

Meeting Costello[]

Costigan arrives at the bar to meet Costello. As he chats with Costello about FBI relations, Costello reveals that there's a "rat" in his group, surprising Costigan. While Costigan shits his pants, Costello begins showing off his Beretta 84B Cheetah to Costigan and running drugs through the city. Frank leaves.

Captain Queenan murder[]

Two days later[11], he calls Captain Queenan. As Queenan goes on the train, he sees Costigan, commenting that Queenan has a tail but Queenan explains he doesn't. However, Sullivan ordered some Internal Investigations cops to stalk Captain Queenan, to find out if he went to the infiltrator and tell Costello who he is. As they leave the train, they separate and Costigan texts Queenan to meet him at 344 Wash. On the roof, Costigan informs Queenan that Costello will find out his true identity and will kill him. Queenan requests that they will figure out what to do. As Billy receives a call from Delahunt, telling him to meet at 344 Wash. Realizing this, the two try to escape. Unfortunately, the crew are already in the building and heading up. Queenan orders Costigan to escape as he attempts to negotiate with them. As Costigan escapes, Queenan falls to his death, landing in front of Costigan. As Costigan is over Queenan's body, Fitz, Delahunt and the rest of the crew sees Costigan and orders him to get in the van, only for them to be shot at the Internal Investigations Unit officers, with a wound on Delahunt.

Delahunt death[]

At the hideout, Fitz goes at Costigan of his whereabouts. As Costigan explains, Delahunt, on the couch and badly wounded, calls for Billy. Costigan goes over and Delahunt revealed that he mistakenly gave Costigan the wrong address (he told him 314 Wash), but Costigan came to the right one indicating that Delahunt know Costigan's true identity, Costigan attempts to pull out his gun and kill him but Delahunt goes on asking Billy to tell him why he didn't go there before he gargles under his throat and dies. Costigan feels his pulse and leaves the hideout.

Call from Colin[]

As Costigan is drinking in deep depression, Colin calls him from Queenan's blood-stained phone. Suprised, he packs up his stuff but he decides to contact back. As he calls Colin, Colin says that he is taking over Queenan's unit and asks for Dignam but Colin reveals that Dignam is on a leave of absence. Colin asks to meet him but Billy hangs up.

Ambush in Sheffield[]

During the withdrawal of cocaine in a crate, in a warehouse in Sheffield, Costigan sends Colin a message of Costello's crew whereabouts. At the deal, Costigan escapes as the crew are ambushed, in which there is a shootout between the police and the mobsters, which will cause the death of most of the mobsters, including French, who while backtracking with the car, slams and shoots himself in the neck shortly before the car explodes. Meanwhile, Costello gives in to his escape, and is joined by Sullivan, who asks him about the FBI and Costello tells him that he wouldn't report him because he's like a son for him, but Sullivan teases him and after dodging Costello's shot kills him.

Encountering Colin and the Tape[]

Costigan meets with Colin at the SIU headquarters. As he asks Colin for a favor to find Costello's rat and arrest him. And as Colin recovers Billy's police record, revealing his information, Costigan finds the "citizens" envelope under Colin's files and he leaves. Colin comes back to his office to find Costigan gone and the "citizens" letter on show he then accesses Billy's record and erases it. Later, Costigan encounters Madolyn in front of Colin's apartment and he gives her a disc. After Madolyn discovers the disc is a conversation between Colin and Costello she silently enters the bedroom and despite Colin's plea's does not come out Sulivan thencontacts Costigan, who revealed that Costello recorded everything for evidence for the FBI and Costello's lawyer came to Costigan about the disc. As Costigan taunts Colin since he is the mole of Costello, he tells him to meet at 344 Wash at 3:00 PM, where Queenan was killed.

Attempted Arrest and Death[]

At the meeting, Costigan ambushes Colin and pistol-whips him. Costigan handcuffs him and Colin reveals that he erased Costigan's record. As they are about to leave, Trooper Brown comes up the roof and draws his gun. As Brown orders Costigan to drop his weapon and step away from Sullivan, Costigan refuses and explains that Colin is Costello's rat and has evidence. As they head for the elevator, Colin's anger expresses if they land into jury. Sullivans begs Costigan to kill him, who replies "I am killing you", meaning Sullivan's career and his relationship. As they exit out the elevator, Costigan is shot in the head by Trooper Barrigan, who shoots Trooper Brown when he discovers Costigan's body. Barrigan reveals to Colin that he was also a mole for Costello and Colin kills Barrigan in response confirming his preference to a police life and desire to change. When Costigan, Brown and Barrigan died, Colin is rescued by the police, he wanted to nominate Billy for the medal of merit.


Billy Costigan enrolls at the Massachusetts State Police Academy to become a trooper, wants to become a member of the state police, but reluctantly learns that he will never be able to become a state trooper, despite the fact that he never committed crimes related to the mob, because of his connections with the Irish mob in Boston, even if he hears and knows he is not part of it. He was forced to live in two worlds, one at the weekend with his father in Southie, and another in the upper middle class in North Shore with his mother. From an early age his family had a split, from the divorce of his parents, cutting ties with his relatives. This has influenced his youth. Billy has experienced times that have made him emotionally vulnerable. Despite does not become a trooper, he will be caught by Captain Queenan and Staff Sergeant Dignam as an infiltrator in the Irish mob, thanks to his connections there. Billy worked for Frank Costello for months, and lived as much as he can to infiltrate life, knowing that Costello could find out he was the mole and kill him at any time, making him feel stress, anxiety or anger, even taking pills. Billy, however, is willing to do all he can to continue his mission and finish the job, managing to convince Costello, when he was accused by him of being the mole, of not being him the mole. When he finished his mission, he wanted to quit his job as a cop, and get his identity back, which he hid during the infiltration period. When he finds out that Colin Sullivan is the mole in the police, he tells Madolyn, who despite being engaged to Sullivan, had developed a hidden love even with Costigan before proving it to everyone. He brought him the remarks of the speeches of Costello and Sullivan, which had been entrusted to Billy, because Costello trusted Billy for more than anything else. Afterwards he wants to meet Colin on the roof of the 344 Wash, because he wants to arrest him, but then he discovers that Colin has eliminated his file, and therefore he is no longer part of the police. Billy then brings Sullivan into the elevator, after intervening Brown, who is incredulous of the situation. Shortly before arriving on the ground floor, Colin tells him that he prefers to be killed, rather than watching his fall. Billy says his last words: "I am killing you", in the sense that by demonstrating his accusations with the proofs that Costello gave him, he will collapse ruinously, he will lose his desire to always aim high. After Costigan, Brown and Barrigan died, Sullivan plans to register Costigan for the medal of merit. It could’ve been an 'act' to convince his superiors or maybe Sullivan appreciated the sacrifice that Costigan made for the Police, one he never got a chance to do.



  • Originally Tom Cruise was planned to play Billy Costigan.
  • Leonardo DiCaprio gained fifteen pounds of muscle for his role as Billy Costigan.
  • Leonardo DiCaprio was one of the three Oscar winners, along with Jack Nicholson and Matt Damon.
  • Leonardo DiCaprio called his one-on-one scene with Jack Nicholson "one of the most memorable moments of my life."
  • Leonardo DiCaprio described Billy Costigan as being in a "constant, 24-hour panic attack.".
  • Leonardo DiCaprio called Billy and Colin "two sides of the same coin".
  • He is inspired off of the undercover officer Chan Wing-Yan, of Infernal Affairs (2002).
  • Tom Kemp plays Billy Costigan, Sr. and Zachary Pauliks plays Billy Costigan, Jr. as a child. A scene had been recorded in which Frank Costello spoke to Billy's father who was cut, but it is possible to see them in the film in a photo.
  • When Billy and Frank are sitting in a bar, Billy is just sitting at the table. In the next shot he's suddenly in the middle of blowing smoke rings into the air.
  • Billy's telephone number is 617-869-1469, seen when Colin calls him, but when Billy calls back from that same phone a couple of minutes later, the calling number shows as 617-177-9528, which doesn't match.
  • The trailer shows the part where Sullivan accesses Billy's file. In the trailer the social security number is 135-01-6629, while in the film it is 229-00-8003.
  • The first time Colin Sullivan accesses Billy's file, his date of birth is November 7, 1984, but when he re-enters the file the second time, the date is November 7, 1980.
  • Between the discovery by Costigan of the envelope on Colin's desk, and the return of Colin in the room, the arrangement of the various piles of documents on the desk have changed.
  • On the envelope Madolyn receives, Billy's return address is on Conant St. in Boston, but Conant St. is in Revere.
  • When Billy is arresting Colin, he says "you didn't come here to talk, you came here to get arrested" but his mouth is not moving.


  1. "Costigan, William M" Seen the middle name or the initial of it, while Colin accesses Billy's file.
  2. 2.0 2.1 Is seen in Billy's file.
  3. The murder of Myles Kennefick takes place on September 19, 2006, making The Departed set in 2006. At one point in the film, during a meeting with Queenan and Dignam, Billy Costigan mentions that a year has passed, coming to 2007. In the Colin phone "Mar 16,06", or March 16, 2007 (2006, it is a plot error, as Kennefick died in September of this year). On this day the affair between the Chinese mob and Costello takes place. They pass six months, expressed by Billy, four from the Chinese deal. The events that follow take place day after day, and Billy Costigan's death takes place eight days after the deal (16), making it July 24, 2007.
  4. "Costigan, Catherine R." it is written in Billy's mother's pills container, seen while Billy is in her apartment.
  5. "And I'll forget your grandmother was so nice to me." Expressed by Mr. French to Billy.
  6. "That maggot uncle of yours... Tommy Costigan, is another goof." Expressed by Staff Sgt. Dignam to Costigan.
  7. 7.0 7.1 Is seen in the database in the movie.
  8. "And one priest" Expressed by Costigan to Staff Sgt. Dignam.
  9. Is the 12-year-old boy who married his uncle priest John Costigan.
  10. "I got kicked out, like, four months ago." Expressed by Billy Costigan to Aunt Kathy Costigan.
  11. "Like I said, two days ago my guy damn near found out who Costello's rat is. But he lost him in the streets." Expressed by Captain Queenan to Colin Sullivan.