Cazale's entire career is only five movies:
The Godfather, in which he had a very small role as playing the only Corleone brother you didn't care about and fumbled his gun when Vito was shot down.
The Conversation, which is the only one I haven't seen.
The Godfather Part 2, where he basically sells out his own brother and ends up getting killed by said brother's orders in the end.
Dog Day Afternoon, where he becomes the fall guy for Al Pacino's bank robbery. He thinks Wyoming is another country and is completely unaware that Pacino is plotting with the cops to ensure his own safety, and ends up being shot right in the head.
The Deer Hunter, in which he plays the guy who always forgets his boots when they go hunting. He carries a gun and none of his friends really like him. He's basically one wrong move in front of DeNiro on a hunting trip from being capped in the mountains. In real life, he died after filming The Deer Hunter. He even knew he was dying while the movie was being filmed and he still managed to pull off being a sleazeball.
Can you imagine, with today's media how crazy that death would've been? Here's a man who obviously found himself in some classics and the sky was the limit for him in a Heath Ledger sort of way, who's life was cut short by awful awful cancer.
Today, John Cazale seems so forgotten. Sure we always remember him in the heart wrenching moment when he's teaching Michael's kid to say Hail Marys before they go fishing, or when he's the only one at the dinner table who's proud that Michael decided to fight for his country in World War 2, but we never really think of his talent and what could've been. Those memories tend to go towards the lesser actors of that era who had serious drug problems (won't name names out of respect for fat comedians).
My pieces on film indeed stretch over many topics, but sometimes you just have to sit back and appreciate those who never seemed to be truly appreciated, and John Cazale gets the award for "Most Underrated Tragedy of All-Time." A fantastic actor, and a death that he couldn't do anything about. There aren't any Betty Ford clinics for cancer friends.