The idea of creating a shared film universe for Marvel characters was born in the late 1990s. Marvel wanted to bring the successes of its comic book characters to the big screen and decided to produce several films that would form a coherent universe. Phase 1 of the MCU officially began in 2008 and marked a milestone in film history. Kevin Feige, President of Marvel Studios, was instrumental in its planning and implementation.

Summary of the plot of Phase 1 of the MCU:

1. Iron Man (2008) : Phase 1 kicked off with "Iron Man," a groundbreaking movie that introduced Tony Stark (Robert Downey Jr.) as a genius weapons manufacturer. After his imprisonment in Afghanistan, Stark develops the Iron Man suit and decides to change his life. The movie lays the foundation for the MCU and introduces viewers to the post-credits scene that would become a hallmark of MCU movies.

2. The Incredible Hulk (2008) : This movie presents Edward Norton as Bruce Banner, who transforms into the Hulk when he gets angry. The movie depicts Banner's escape from the government and the search for a cure for his transformation. Although not as successful as other MCU films, 'The Incredible Hulk' adds to the overall storyline.

3. Iron Man 2 (2010) : Tony Stark takes center stage as he is confronted with his identity as Iron Man. New characters such as Black Widow (Scarlett Johansson) are introduced, and the plot lays the groundwork for events to come in the MCU, particularly by hinting at the formation of the Avengers team.

4. Thor (2011) : "Thor" introduces the viewer to the mystical world of Asgard. Thor (Chris Hemsworth) is banished to Earth and must learn to use his powers responsibly. The film establishes the character Loki (Tom Hiddleston) as a central figure in the MCU and connects the cosmic elements of the universe with the earthly ones.

5. Captain America: The First Avenger (2011) : The film transports us to the time of the Second World War and tells the origin story of Captain America (Chris Evans). Steve Rogers becomes a superhero thanks to the Super Soldier Serum and fights against the evil Red Skull. The movie also shows Rogers being frozen in ice, which is crucial to the future of the MCU.

6. The Avengers (2012) : 'The Avengers' was the epic finale of Phase 1, directed by Joss Whedon, which saw Iron Man, Captain America, Thor, Hulk, Black Widow and Hawkeye united as one team to fight Loki and the alien threat of the Chitauri. The film was a huge success and cemented the concept of the joint MCU.

Overall, Phase 1 of the Marvel Cinematic Universe laid the foundations for a cinematic experience that had never been seen before. By linking characters, storylines and an exciting interplay of action, humor and emotion, the MCU established itself as a unique and fascinating cinematic universe.