Character Analysis
The Taker
Frank Costello has one major motto in life:
COSTELLO: No one gives it to you. You have to take it.
Frank, who's based heavily on real-life South Side gangster Whitey Bulger, isn't interested in playing by the rules of the society around him. And this might have something to do with the fact that he's an Irish Catholic who grew up during a time when the Irish were hated in America. The dude has a big chip on his shoulder—and a massive ego to go with it. For Frank, life is all about taking whatever you want and daring other people to try and stop you. And when these people do try and stop you, you kill them.
If there's one thing that Frank doesn't really have time for, it's people who don't share his sense of ambition. In the case of Billy Costigan's dad, Frank has a begrudging respect for the guy. But at the same time, he notes that Billy's old man:
COSTELLO: ...never wanted money. You can't do anything with a man like that.
In other words, Frank feels like Billy's father never had a real chance to participate in the American Dream because he never had the guts to go out and take what he wanted. Frank applies a similar logic when he considers whether to let Billy into his crew, saying:
COSTELLO: [You] can't trust a guy acts like he's got nothing to lose.
For Costello, you always have something to lose, and anyone who suggests otherwise is just bluffing.
A Legacy Man
Despite his belief in doing anything to get what he wants, Costello still follows a certain honor code. For example, he feels a bit bad about bringing Billy Costigan into his criminal world, saying:
COSTELLO: Your Uncle Jackie, he also would kill my entire f***ing family if he saw me here with you. And I think about this.
Costello then asks Billy:
COSTELLO: Did you ever think about going back to school?
At this point, Frank seems to be doling out some genuine fatherly advice, and he's disappointed when Billy doesn't listen to him.
You see, Frank Costello has a fatherly streak in him. Maybe it's because he needs someone to carry on his legacy. We don't really know, but we do know that he takes both Colin and Billy under his wing because neither of these guys has much of a father figure in his life.
Colin challenges Frank directly about his fathering tendency toward the end of the movie when he asks:
COLIN: Is that what this is about? All that murdering and f***ing, and no sons.
This obviously strikes enough of a nerve for Frank to try and kill Colin, but the guy only ends up getting shot and killed himself. In the end, Costello knows that the only way to truly satisfy his ego is to create a miniature version of himself to carry on after he's gone.
Victim of His Own Fuzzy Feelings
As a mob king, Frank likes to think of himself as totally irreplaceable. As he tells Billy:
COSTELLO: The only one who could do what I do is me. A lot of people had to die for me to be me.
He also reminds Billy that in times when he can't trust anyone, he tends to wipe out everything around him:
COSTELLO: You know, past days, situation like this, I kill everybody. Everybody who works for me.
Of course, we have to ask the question—why are things different this time? Won't Frank just end up killing everybody again as soon as he starts to feel a little heat? Well, we're not sure. The thing is, this time around, we get the sense that Frank's too emotionally invested in Billy and Colin to wipe them out. After all, these guys are his legacy. And it's this fatherly pride that ends up causing Frank's downfall when Colin shoots and kills him.
You can't really be a mob boss if you start getting attached to people. There's a reason, symbolically, why Frank never was able to have kids before: the life path he has chosen is sterile. That's a lesson he finds out too late.
P.S. Did you notice that Frank's ultra-paranoid, too? That's a common theme in Scorsese's work: think about Joe Pesci's character in Casino and Ray Liotta's character in Goodfellas.
Frank Costello's Timeline