Iron Man (2008)

Directed by Jon Favreau, who played Happy Hogan a main stay character in the Iron Man franchise within the MCU. The movie was released on May of 2008, just 2 months before the release of Christopher Nolan's highly anticipated Dark Knight, the follow up to Batman Begins. In the weeks leading up to the Dark Knight, Marvel Studio's gamble on Iron Man paid off, the film made a profit. Iron Man (2008) made back double the cost of its $140,000 budget domestically, and accumulated slightly over half a billion dollars world-wide.  With Producers Avi Arad, Jon Favreau, Peter Billingsley, Louis D'Esposito, Kevin Feige, Stan Lee, and a few others behind it. Marvel Studios was now in a position to command more talent and resources.
In 2004, Avi Arad had taken out a large loan, on par with the world wide Box office total of Iron Man to in-house create 8 Marvel franchised movies over 10 years, this was in part due to profitability and the returns of Daredevil, Blade, (Sony's Spider-Man), and Elektra and that its vault of characters could be sustainable, and with the financial returns of Iron Man, Marvel Studios was re-born.
In 2009, Disney who initially passed on buying Marvel around 2004, bought Marvel Studios for $4 billion; and under Kevin Feige and Louis D'Esposito leadership Marvel Studios continue to run an economically sound flag ship franchise. With Favreau being an executive producer for Star War's Mandalorin , another of  Disney recently acquired properties.

Jon Favreau, Kevin Feige, Louis D'Esposito (left to right)

Iron Man is an origin story of Tony Stark, it was the film that first condition its audience to stay to the end of a films post credit scene, when the name Samuel L. Jackson as  Nick Fury appeared when credits began to roll it caught fire by word of mouth to stay for the end of the credits. Now to say watch Iron Man and then Endgame would make no sense, it would be as if the world itself had lost it's mind. Iron Man laid the ground work of an 11 year odyssey of  21 separate stories that all lead to the Endgame.
With a high caliber cast - Jeff Bridges, Gwyneth Paltrow, Robert Downey Jr., and Terrence Howard, it was revolutionary, it was nominated for two academy awards, for best sound editing and best visual effects, a first for Marvel towards having a property being excepted in mainstream Hollywood. It was also different because it was not driven by green screen special effects, everything Downey interacted with was actual present and before him. Using the pages of the comic book as a skeleton, Favreau allowed the actors to improvise. To provide the actors a chance to give their characters more life and realism than what sometimes maybe ridged on the page, you got a rapport of his girl Friday between Downey Jr. and Paltrow, and wonderful on screen banter between the full cast of characters who now seem to know each other for years.