It's unreasonable to watch all 21 Marvel movies before heading out to see Avengers: Endgame, but some of them are just essential to have in the back of your head going in to the theater.
These are the five MOST important Marvel movies to watch ahead of Endgame...
1- Iron Man
The one that started this whole thing. 2008's Iron Man starred Robert Downey Jr (could you imagine ANYONE else in that role?) and set off a journey that culminates this weekend in Avengers: Endgame. The story revolves around billionaire arms dealer, Tony Stark, realizing that his weapons are killing millions and wanting to help instead of hurt.
Iron Man is currently streaming on the Syfy app (if you have a cable subscription)
2- The Avengers
The 2012 movie first saw all out heroes together for the first time, in what ended the "First Phase" of Marvel movies. Thanos is mentioned, and the events of this movie begin a chain reaction of events that get us to the Endgame. The "attack on New York" is referenced several times in movies after this. It motivates our heroes to never have regular citizens attacked like this again. It fuels Tony and ends up haunting him going forward.
The Avengers is available to rent on Amazon, iTunes, YouTube, etc
3- Avengers: Age of Ultron
Ultron isn't a great movie. In fact, it's maybe the worst movie in the MCU, in my opinion. Hot take, I know, Thor: Dark World is probably worse, Hulk too. But there is one critically important scene. And I've attached it above! The phrase "Endgame" is first uttered and it may be a big clue to how Endgame ends. The riff between Cap and Iron Man grows here.
Avengers: Age of Ultron is streaming on Syfy if you want to watch the whole movie.
4- Captain America: Civil War
The third movie in the Captain America series, is essentially an extra Avengers movie. All our characters take sides and feud over the government wanting the heroes to register and only act if called upon. Tony Stark likes the idea because the weight of being Iron Man is beginning to be too much. Captain America hates the idea because it takes away his freedom. Can the beef be squashed in time to save The Avengers?
Civil War is available to rent on Amazon, iTunes, YouTube, etc.
5- Avengers: Infinity War
I mean, obviously. Right? Avengers: Endgame is actually the second part of Avengers: Infinity War. A move to make Disney an extra billion dollars, yes! But it gives as an epic ending. The snap heard 'round the world creates a tragic ending. As the villain from the first Avengers movie comes back to conquer Earth. An emotional ending setting us up for the most anticipated movie of all-time in Endgame.
Infinity War is streaming on Netflix.
Honorable Mention if you have more time
- Guardians of the Galaxy
- Ant-Man and the WASP (Streaming on Netflix)
- Iron Man 3
- Captain America: The Winter Soldier (not because it's connected, I just think it's the best of these 20+ movies)