You still don’t know him unless you’re a total cinephile geek (which hopefully many of you are), but John Cazale only starred in five movies and each one of those films — “The Godfather,” “The Godfather II,” “The Conversation,” “Dog Day Afternoon” and “The Deer Hunter” — was nominated for an Oscar Best Picture. In fact, the five films garnered 40 nominations in total, but Cazale, the subtle, mannered and wiry actor best known for playing Fredo Corelone in “The Godfather” films was never once nominated.

 Tragically, his life was cut short after he died of cancer at the age of 42. At the time he was dating Meryl Streep and had worked toe to toe with the giants of 1970s cinema, both in front and behind the camera. Director Richard Shepard (“The Matador,” “The Hunting Party“) was a longtime fan of the underappreciated actor and in 2008 started mounting a documentary about him. Titled, “I Knew It Was You: Remembering John Cazale,” the economic 40-minute documentary premieres on HBO tonight at 9:00 p.m. EST. We caught up with Shepard this weekend and discussed the understated brilliance of Cazale, the misinformation surrounding the actor’s life, his relationship with Meryl Streep, how Brett Ratner got the film made and why Michael Cimino, director of “The Deer Hunter,” is a fool for not appearing in the documentary.

Why make this doc?
Honestly, John was always my favorite actor from even when I was a kid, I just loved him. I remember my dad taking me to the Bleecker Street revival theater and showing “The Godfather” movies to me like when I was 14 or 15. I just loved him and didn’t even really know why, it’s so funny cause whenever you really think about the characters he plays — Fredo is like a pimp and a low level scumbag, but somehow I really responded to him and I think it was, there was some sadness in him. I think I was always a film geek and I would watch “Dog Day Afternoon” and at certain point I started putting it together that it was the same guy, it wasn’t an instantaneous connection.

And I think by the time I went to NYU film school in the early ’80s it was just sort of that thing — the answer to the question who your favorite actor is this guy that most people were like, “who?” and I sorta became this cool thing to talk about it, plus he was in five of my favorite movies of all time. But as I got older I realized that it was more than just a young shtick, he really is such a phenomenal actor and all through my professional life and everything I’ve ever done, I’ve always talked about him with other actors and directors and always got a great response and I sorta realized that anyone who knows anything about film or acting loves this guys — even if it is a specific type of film geek thing — but there is something about him that affects people.

There’s a lot of misinformation about him out there. Most people think he died of bone marrow cancer when he actually died from lung cancer and of course there’s fallacies about his relationship with Meryl Streep.
Its true, it’s weird. A few years ago I wanted to learn more about him and there’s so little information out there and a lot of it was wrong. They say he was engaged to Meryl Streep, which was not true. So at some point I thought maybe someone should make a documentary about him and then I realized that I was in a position to do that even though i had never made a documentary. To be honest with you, it started out as a detective story, I didn’t know anything. Half of the first interviews I was excusing myself because I asked some really rudimentary questions. A lot of time documentaries know the answers to the questions they’re asking and they’re just looking for talking heads to expound on the subject and that was not the case. I literally asked Meryl Streep, “so you were engaged to him,” and she was like, “no.” [laughs ].

The picture is much more a portrait of his work, the acting than it is about his personal life.
It was a detective story along the way and in a weird way I think it ultimately helped the movie cause I wasn’t really sure what the angle of it would be about. And at a certain point, Meryl said she learned acting from John and Al Pacino basically said the same thing and then I realized the movie was really going to be about his acting, because he has an interesting story — yes, he died young, yes, he was with Meryl Streep which is obviously very interesting — but really his legacy is not his personal life, his legacy was that he was an absolutely fine actor who happened to work many times with the best actors of that generation and in a way and helped participate in the best performances they ever gave.

It’s funny cause your experience mirrors many other film geeks experiences when you’re a teenager and then come to realize he was in the five best movies of the ’70s.
His run was incredible. I have joked subsequently that if he had lived his next film would have been the “Bad News Bears in Breaking Training” or something, at some point probably his streak of classics might have ended. But he wasn’t just a guy that happened to appear in those five movies, he was just amazing in those films and that’s what struck me. In in a weird way, he’s not the lead in any of those movies — his time on screen is limited, but somehow that draws you in even more. He has a few histrionic moments in “The Godfather II,” but in general he doesn’t. His acting is much subtler, so in a weird way his performances grow each time you see it, as opposed to someone who is over the top or at least showboaty and you kinda get it the first time you see it. I also think that he helped these other actors tremendously. I think there’s a reason that Pacino worked with him in three movies and a bunch of plays and Coppola did three movies with him. He made everyone else better and he made them absolutely real.

He’s a cult figure. You either have no clue who he is or you cherish and adore his work.
I agree. there’s a whole cult of people who’s favorite movies are those who do know John. The response I received from this film at film festivals we’ve been to without a doubt is great. I get emails from people everyday from people who say, thank god you’re making this movie and that’s like, ‘wow, that’s cool.”

What made Cazale stand out in your mind other than the obvious?
Supporting actors will try and overdo stuff so that they will get camera time and I’ve noticed that so many times and it’s just like “just take it down a fucking notch, I’m not cutting to you, and especially not when you’re doing stupid stuff.” But John never did that I think he was always in the employment of the moment, you know he was a very moment to moment actor and those are the best actors because they — John was so great at reacting to other performances. Most of his performances, especially “Dog Day Afternoon” are just him reacting. It’s all about him being in that moment, like just full blown in that moment. He really supports and elevates the other performances, he’s just kind of wonderful in that way. John was always about the moments that are not highlighted in a script. And that was a big acting lesson to everyone around him; how to react. I think he went, I mean Meryl Streep says and I truly agree with her, he went so deep into these characters, he literally just appeared. I don’t think — the idea that the guy playing Sal in “Dog Day Afternoon” is the same guy who played Fredo [in “The Godfather”] is almost impossible to see that. I mean there’s sadness without a doubt in both characters but it’s like he fully reinvented himself.