Character Analysis
Trapped between Two Worlds
One of the first things we learn about Billy is that he comes from the rough neighborhood of Southie in South Boston. As Sergeant Dignam puts it:
DIGNAM: So you have family connections down in Southie, right? Through your father?
But Dignam is quick to follow this question with another question:
DIGNAM: Why don't you tell us about your Uncle Jackie?
Yeah, that's because apart from his father, Billy's connections in Southie are all criminals. His Uncle Jackie was a major player for the Irish mob before the mafia had him killed.
On the one hand, these connections make us wonder about how suitable Billy would be as a cop. But on the other hand, Dignam and Captain Queenan realize that Billy's Southie connections can be put to good use if they use him as a police informant in the area.
It's fair to say that Billy's relationship with his family is not good. For starters, there seems to be a major split between his father's side of the family and his mother's. His mother, you see, was from a wealthier family from a better part of town; she eventually divorced Billy's father and raised Billy in the Northern part of Boston. And we can see the effects of this class division when we learn that no one from Billy's mom's side of the family went to his father's funeral except one cousin named Stephanie. Billy calls out his Uncle Edward on this when he angrily asks:
BILLY: Stephanie, who was the only one who came to my father's funeral?
He quickly follows this up with:
BILLY: When my mother dies, we don't have any more connection.
It's clear from the start of this movie that Billy's a guy who's trapped between two worlds. Growing up, he was trapped between the worlds of the wealthy North Shore and the rough Southie. And now that he's all grown up, it looks like he's going to get trapped between the world of the police and the world of criminals.
That's right: he's chosen to go undercover to help break up part the Irish mob. As an undercover police informant, he spends most of his time between two worlds, never really belonging in either of them.
Losing His Marbles
After he goes to work as a police informant, Billy realizes that being an undercover cop is a stressful gig, especially when the dude you're investigating might kill you at any moment. So how does he deal with this life, we might ask? Well, according to Billy, the secret is to totally separate what's happening on the inside from what's happening on the outside. As he puts it:
BILLY: That's one thing I figured out about myself in prison. My hand does not shake. Ever.
That said, Billy knows that he's going to lose his mind if he doesn't get out of his job soon. When his counselor Madolyn denies him Valium to help him sleep, he goes nuts and says:
BILLY: Why don't you just give me a bottle of Scotch and a handgun to blow my f***ing head off?
Even though Billy is good at handling stress, he's still a human being. And after more than a year of working undercover, it makes sense that the guy would get pretty burned out.
There are only so many times that Billy can throw Frank Costello off his scent. Eventually, Costello outright accuses him of being a rat, and Billy knows that it'll take a major gamble to convince Frank that he isn't. So he uses all of his smarts to say,
BILLY: You pressure me to fear for my life and I will put a f***ing bullet in your head as if you were anybody else. Okay?
This is exactly the sort of thing that makes Billy successful as an undercover informant. Even though he's scared of being killed, he's willing to risk everything for the sake of maintaining his cover. If he had just played things safe all the time, Costello would probably have killed him long ago.
Trickster
Billy is a risk-taker, but he's also a master of deflection, which means he's good at getting Frank to think about something else whenever the question of Billy being a rat comes up. When Frank asks him about the rat, for example, Billy subtly changes the subject by appealing to Frank's pride and saying:
BILLY: The question is, and this is the only question—who thinks that they can do what you do better than you?
By asking this question, Billy actually takes the focus off himself without ever making it seem like he's changing the subject. And that's something that a master liar knows how to do really well.
Despite all his success, Billy knows that Frank Costello will eventually find him out and kill him. That's why he can't believe the police are taking such a long time to arrest the guy. Or as Billy puts it:
BILLY: The guy f***ing murders somebody and you don't f***ing take him! What are you waiting for? Do you want him to chop me up and feed me to the poor?
It's times like these that remind us how emotionally vulnerable Billy is, and these are moments that make it easy to identify with the guy. If Billy were just Mr. Cool all the time, he wouldn't really be believable as an undercover cop. But Martin Scorsese knows how to get us on board with his protagonist, and that's why we root so hard for Billy throughout this movie.
Billy Costigan's Timeline