The casting of Robert Downey Jr. as Tony Stark is now considered one of the greatest decisions in cinema history. However, Marvel executives initially pushed back hard against Jon Favreau's recommendation due to RDJ's past struggles. Favreau fought for him, insisting he was the only actor who could capture Stark's genius and arrogance.

It's easy to forget that before 2008, Marvel was recovering from bankruptcy. They had sold off the film rights to their most popular characters—Spider-Man to Sony, and the X-Men to Fox. They were forced to build their cinematic universe using the "B-tier" characters they had left, like Iron Man and Thor.

Stan Lee's legendary cameos became a staple of every Marvel movie. In 2017, to accommodate his declining health, James Gunn filmed four different Stan Lee cameos in a single day against a green screen on the Atlanta set of Guardians of the Galaxy Vol. 2, banking them for future films.

Keeping the plot of Infinity War and Endgame secret was a monumental task. Actors like Tom Holland and Mark Ruffalo were notoriously bad at keeping secrets. To combat this, the directors handed out fake scripts. Holland didn't even know who he was fighting during the massive Endgame battle—he was just told to punch the air.

The sheer scale of Avengers: Endgame broke records before it even hit theaters. The production budget was estimated at nearly $400 million, making it one of the most expensive films ever made. The investment paid off when it temporarily dethroned Avatar as the highest-grossing film of all time.

The collaboration with Sony to bring Spider-Man into the MCU was a historic legal and creative achievement. When the deal temporarily fell apart in 2019, Tom Holland reportedly called Disney CEO Bob Iger while slightly intoxicated at a pub, making an emotional plea that helped bring both studios back to the negotiating table.