Avengers: Endgame

Avengers: Endgame is where the epic battle for the Infinity Gauntlet finally comes to an end, and arguably its most shocking moment is when one of the franchise's most important characters, Iron-Man, is killed. This film sets itself apart from others because it wasn't afraid to take risks with the loss of integral characters, and it wraps up the Avengers story in a realistic way. 

The Avengers

The 2012 Avengers kicked off the entire series with the introduction of Iron-Man, Captain America, Black Widow, Hawkeye, and Hulk teaming up for the first time. This movie also set the stage for subsequent spin-off movies dedicated to individual characters. Building a whole universe around this team was a genius move by Marvel.