The Guardians of the Galaxy made their debut to the MCU in the 2014 movie of the same name, but that wasn't always the plan.
"We toyed with the idea of doing short films on Drax, on Rocket and Groot, and on Gamora, leading up to Guardians," Marvel Studios boss Kevin Feige revealed in the recently published book The Story of Marvel Studios: The Making of the Marvel Cinematic Universe (via ScreenRant).
In the movies, Drax is played by Dave Bautista, Rocket and Groot are voiced by Bradley Cooper and Vin Diesel, while Gamora is played by Zoe Saldana.
"This One-Shot series would have led into the Guardians movie proper – which would have also been directly preceded by a fourth self-contained short film about a mysterious kid who loved fantasy things. Then you'd start Guardians. And half-way through, we would reveal that big space hero is the kid from the short. We thought that would be clever, but it was too much."
The "big space hero" is, of course, Star-Lord, played by Chris Pratt. As for one-shots, Marvel hasn't released any since 2014 – titled All Hail the King, the studio's last short told the story of Trevor Slattery (Ben Kingsley) after the events of Iron Man 3. Others featured Agent Phil Coulson (Clark Gregg) and Agent Carter (Hayley Atwell), telling short-form stories that fit in between the MCU's main movies.