Actually, I've been thinking about it for a long time. It doesn't matter how much is behind except Iron Man. Iron Man appears in the last three films, so you don't watch Iron Man 1, and you don't even know who he is when he appears later.

Let me tell you a few shots.

In Iron Man 1, at the end, all the letters are released, and the shield appears, inviting Stark to join The Avengers.

In iron man 2, there is a scene in the middle that enters Captain America's Shield. At the end of the film, the Cyclops of S.H.I.E.L.D. said that Stark could not join The Avengers because he could not meet the requirements. That is, in the new movie The Avengers, when Stark first arrived, he told them that he didn't meet the requirements, that he was arrogant and narcissistic.

Stark's father starred in Captain America. At the end of the film, S.H.I.E.L.D. unfrozen Captain America from decades of sleep and let him join The Avengers.

In Thor, Thor just came to Earth, and the agent (the one who died in The Avengers, the one who asked Captain America to sign it) mentioned Stark and called Stark to ask him if he made it.

Hulk, Stark appeared at the end of Hulk's film and told the general that he had always opposed direct human testing. He still thought it was better to upgrade the hardware.

I don't remember the rest. Actually, it depends on these messy things. There are two animations, which are also quite messy. One is Hulk vs Raytheon, and the other is Hulk vs Wolverine.