Martin Scorsese has been behind the development of no small number of great actors. For instance, if it weren’t for him, Robert De Niro would not be the actor he is today. And, as the director’s new film Shutter Island will confirm, if not for Scorsese, Leonardo DiCaprio wouldn’t be one of the best actors of his generation.

While DiCaprio has been a household name since the mid-1990s, he has not always been considered a serious actor. His role in Titanic confirmed him as more of a heartthrob than a thespian to be taken seriously, and, with only a few good films here and there, DiCaprio initially seemed destined for a short-lived career.

It was in 2002 that the actor finally gained recognition, and from two of Hollywood’s top directors no less. DiCaprio’s appearances in both Steven Spielberg’s Catch Me If You Can and Martin Scorsese’s Gangs of New York initially garnered skepticism — after all, most audiences were exclusively familiar with the actor through his character in Titanic — but the release of both films presented audiences with a completely different star.

No longer just an uncomplicated picture of adolescence, DiCaprio began pursuing problematic roles in which characters had their youth but found themselves unable to enjoy it, usually because of inner turmoil.

While Spielberg’s film presents dramatic emotion, it does so in a happier light with only very subtle hints of weariness. It wasn’t until Scorsese’s first collaboration with DiCaprio that the young actor was able to showcase the extent of the inner conflict he could put forth on screen.

At its heart, Gangs of New York is a simple film about revenge. DiCaprio portrays Amsterdam, a man whose father was killed when Amsterdam was only a boy by the ruthless Bill the Butcher. After his release from a reform school, Amsterdam eventually returns to New York to seek his revenge. In order to kill the butcher, however, Ansterdam must first gain his trust to get close to him.

This is where DiCaprio excels — in his ability to convey the conflict between the desire to kill a man while respecting and even loving him at the same time. None of his earlier films allowed him to illustrate such intricacies on screen. He had to work with someone like Scorsese to accomplish this.

As one of the best living American filmmakers, Scorsese has redefined the idea of conflict in film narrative, and it is something he has been doing for over 40 years.

Scorsese’s earlier films like Taxi Driver and Raging Bull, along with his later works such as The Last Temptation of Christ and Goodfellas, all portray characters who are flawed, confused and incredibly conflicted. In an interview with the Los Angeles Times, DiCaprio said, “What Scorsese does so well is when the lead character starts to betray you after a while: After you’re with him, he starts to do things you don’t understand.”

And this sentiment is exactly what has made DiCaprio such a diligent actor since he started working with Scorsese.

In Gangs of New York, Amsterdam starts to love his enemy, and in their next collaboration, The Aviator, the brilliant Howard Hughes gains all the momentum of both aerodynamics and audiences but then loses all of it through blatant misunderstandings and is ultimately ruined.

It made perfect sense for Scorsese and DiCaprio to work together on a film about the life of Hughes because it radiates everything appropriate about their own working relationship. The film personifies personal conflict, and the director and actor thrive off of manifesting cinematic conflict.

To date, The Departed is the best personification of the power these two artists share together, and it is the defining film that has made DiCaprio a great actor.

His character, a Boston state police trooper undercover in the Irish mob, is conflicted between two worlds to the point where he loses all sense of normalcy. By investing himself so thoroughly into a world that lacks morality, he loses his true identity and completely isolates himself from the person he once was.

The Departed, without a doubt, showcases DiCaprio at his very best, and by working with Scorsese yet again, DiCaprio was able to go on and give one incredible performance after another. Without their developed relationship, DiCaprio would not have succeeded in Blood Diamond, Body of Lies and Revolutionary Road.

He would not be who he is today, and Shutter Island would not look as promising. Sure, it is a Scorsese film, and that alone suggests merit. But it is the fact that the film features both a great director and a great actor that gives the film its true momentum.

After all, Taxi Driver would not be Taxi Driver if not for Scorsese and De Niro, and certainly Shutter Island will not be as good as it hopefully is without Scorsese and DiCaprio.