EDITOR'S NOTE: This article is part of a series, "Countdown to Endgame," which looks back at the films of the Marvel Cinematic Universe leading up to Avengers: Endgame.
After revisiting their core three properties to start its second phase, Marvel Studios would introduce its boldest addition to the Marvel Cinematic Universe, all without overt connections to the Earth-bound heroes that had populated the first nine films. And, while embracing the cosmic possibilities of the MCU, the next three Marvel Studios films saw its filmmakers leave clear personal touches on their productions.
This trend would continue for years to come as Marvel started seeking out filmmakers from smaller, independent backgrounds to helm its big budget features, rather than hiring more traditionally prolific directors from film and television. It was these next three films that closed out the middle phase of Marvel Studios' Infinity Saga, with the countdown to Avengers: Infinity War and, eventually, Avengers: Endgame coming immediately thereafter.
Following the initial success of Iron Man, Marvel Studios began assigning up-and-coming screenwriters to adapt lesser known properties, with Nicole Perlman writing a script based on Dan Abnett and Andy Lanning's 2008 relaunch of the Guardians of the Galaxy, Marvel's cosmic team of heroic misfits.
Beating out future MCU directors Peyton Reed and Anna Boden and Ryan Fleck to helm the project was indie filmmaker James Gunn, a selection enthusiastically backed by Joss Whedon, who quietly oversaw much of Phase Two's development.
Gunn completely rewrote the script to match his own personal vision of the film and assembled a cast headed by Chris Pratt, who played Star-Lord. At the time, Pratt was known mainly for comedic roles and had to convince Gunn that he would lose sixty pounds by the time principal photography commenced in July 2013.
Guardians of the Galaxy featured Gunn's signature, irreverent sense of humor and a retro soundtrack handpicked by the filmmaker to add a human element (in a film full of aliens) and reflect its storytelling beats.
Joining Star-Lord on his mission to keep an Infinity Stone out of the hands of Kree zealot Ronan the Accuser was the no-nonsense Gamora (Zoe Saldana), hyper-literal Drax the Destroyer (Dave Bautista), the irascible Rocket Raccoon (Bradley Cooper ) and towering tree man Groot (Vin Diesel).
Despite featuring a relatively obscure cast of characters and no direct links to the rest of the MCU outside of a brief appearance by Thanos and an Infinity Stone, the film was a runaway success, going on to become the highest-earning superhero film of the year and third highest-earning film of the year overall.
The characters were altered in the comics to better resemble their cinematic counterparts, then branching out into other forms of media. Gunn's soundtrack would top the Billboard charts, the first soundtrack album to do so.
Back on Earth, Whedon and Marvel Studios were developing the eagerly anticipated follow-up to The Avengers. Instead of featuring Thanos as the main villain (reserved so that his character could be built up over time), Whedon decided the Avengers should face Ultron, a threat created internally by Tony Stark and Bruce Banner to stoke division and tension within the team.
Naming the film Avengers: Age of Ultron, Whedon decided to include Scarlet Witch and Quicksilver, two characters he had intended to introduce in the original Avengers movie to differentiate the power sets of the superheroes present. Whedon particularly looked forward to Scarlet Witch's inclusion, as her abilities allowed him the chance to explore the psyches' of several characters, including Captain America, Black Widow and Thor.