Executive Meddling: Starhawk was supposed to be turned evil and killed off, but the editors wouldn't let Valentino. His departure allowed Michael Gallagher (who did like the character) to keep him around and redeem him.
DnA for the creative team behind the 2008 series, Dan Abnett and Andy Lanning.
Gotgino (Guardians of the GalaxyIn Name Only) for Bendis run on the series.
What Could Have Been: Jim Valentino has an entire thread here for this Trope. Essentially: Starhawk and Vance Astro would both die, the team would fight Kang and several of their groups of enemies (who would be redesigned to turn them into even more blatant Legion of Super-Heroes analogues), the Protege would turn out to be the Beyonder, and by the end of Valentino's planned run, the group would morph into a Legion of Super-Heroes type organization with a roster of over several dozen heroes.
Ability over Appearance: At first. According to Word of God, Chris Pratt had not lost any weight for his audition - but he was just that good. Nonetheless Pratt did insist on losing 60 lbs to prepare.
In a reddit AMA Alyssa Milano was asked about the ship being named after her - to which she responded "the coolest thing EVER!"
Auteur License: After the seemingly unlikely success of this group of characters, Disney become quite eager to support any adaptation of Marvel Comics characters by Marvel Studios, as made evident by the green-lighting of films like Ant-Man and Doctor Strange which became lucrative new properties in their own right.
Awesome, Dear Boy: Glenn Close was ecstatic to play Nova Prime in, having always wanted to play an M-like authority figure. By all accounts she enjoyed filming the movie and immediately said she was eager to return for a second.
Beam Me Up, Scotty!: Rocket Raccoon is often quoted as saying "I'm gonna need that guy's eye." This is a mashup of two different lines he says at two completely separate points in the film: "That dude, there. I need his prosthetic leg." and "There's one more thing we need to complete the plan. That guy's eye."
Vin Diesel and Bradley Cooper as Groot and Rocket Raccoon respectively. James Gunn did interview professional voice actors at first before opting for a celebrity one. Played with in that this wasn't too prominently displayed in the marketing.
In the Mexican Spanish dub, Rocket is voiced by the Soap Opera actor Sergio Zurita.
In the Japanese dub, the same character is voiced by the comedian Kouji Kato and Groot by scriptwriter and actor Kenichi Endou.
Rocket, Big Time. James Gunn has stated several times that Rocket was a big, if not the main, reason he wanted to make this movie. In fact when it was confirmed Guardians was a hit, Gunn put a heartfelt thank you letter online and specifically thanks everyone for letting a Raccoon make them a little more human.
Vin Diesel loved his character, Groot, so much that he would go to promotions and premieres wearing the stilts he wore for the movie and a shirt proclaiming "I Am Groot."
Defictionalization: It was one thing to put out the Awesome Mix Vol. 1 (it's another thing that it topped Billboard charts for weeks) but to pull this trope and release on cassette.
After arriving on Xandar, Star-Lord flirts with Ti Asha.
Gamora and Nebula demonstrate their Sibling Rivalry by fighting and talking simultaneously, with Gamora emphasizing why she was Ronan the Accuser's first choice above her sister. She then boards a ship full of Sakaarans and kills them.
Rocket Raccoon relays his plan of apprehending outlaws on Xandar to Groot who is merely distracted by a bug.
Denarian Garthan Saal and Corpsman Rhomann Dey argue over where to send the Guardians of the Galaxy with Saal deciding on the Kyln. They also try to fix a malfunctioning light on Dey's armor.
The Mean Guard dances around the Kyln as he listens to "Magic" by Pilot on Peter Quill's walkman.
A montage set to the song "Livin' Thing" by Electric Light Orchestra set after the Guardians escape from the Kyln and before they go to Knowhere. Star-Lord and Gamora are both changing their outfits until Star-Lord makes a suggestive look at her.
Drax the Destroyer explains his tattoos and what they represent to Rocket Raccoon and Groot at the Boot of Jemiah. They get into an emotional argument about mourning the loss of family.
Rocket, Drax, and Groot gamble with a weird alien that has a mouth where his eyes should be.
Stan Lee makes a cameo as one of the exhibits in the Collector's Museum and flips off Groot.
There is a quick vote over whether Rocket Raccoon's laugh can be considered real, to which he retaliates by stating that Star-Lord's plan is not. Gamora agrees that it is not even a concept.
Nebula is shown surviving the battle in Xandar, walking away with a one-armed limp. There is also a quick cut to Peter Quill's Grandfather holding a picture of his daughter and grandson while looking up at the sky on the night he disappeared.
The Guardians of the Galaxy are helped by the people of Xandar after their battle with Ronan, including Broker.
Ronan the Accuser accepts Star-Lord's challenge to a dance off for the Orb.
The pit boss, played by Marama Corlett, had her dialog cut from The Boot of Jemiah bar scene on Knowhere. She was intended to announce the Orloni and F'saki creatures that were seen racing.
Naomi Ryan's dialog scenes were cut for pacing reasons
In order to play Nebula, Karen Gillanshaved her head completely bald and had to endure hours of makeup and prosthetics being applied before cameras could roll. Her hair was then made into a wig and sent to the Star Wars studios (she got it back to film Selfie). She didn't have to go through it all over again for the sequel, though.
Chris Pratt went through an astounding series of physical transformations in the run-up to this film. After spending years as the pudgy Andy on Parks and Recreation he got ripped for Zero Dark Thirty. Then he went back to being pudgy for Parks and Rec before gaining even more weight for Delivery Man. Then he got ripped again for Guardians of the Galaxy winding up sixty pounds less than he was during most of Parks and Recreation. He nearly passed on the project feeling like he couldn't make himself over to get to the body needed for the role, especially after an earlier "embarrassing" audition for one of the G.I. Joe films. But he committed to it and not only got into amazing shape with handsome movie-star looks, he credits it with making his life healthier and better. He also found Star Lord's mask to be extremely claustrophobic and had to deal with panic attacks while wearing it. The fact that the front and back were bolted together (meaning that it was impossible to take off without assistance) didn't help.
Dave Bautista already had the physique to play Drax (though he did say on Chris Jericho's podcast that he had slimmed down somewhat when he came to Hollywood to possibly play more roles than typical Brutes, so he essentially had to bulk back up for Drax) but he had to spend four hours every morning with his arms outstretched as makeup artists applied and colored the 18 prosthetics needed to achieve the look seen on screen. Also, Bautista was wildly enthusiastic about getting a role in a Marvel movie but didn't have much acting experience so he threw himself into acting classes to prepare.
Vin Diesel decided that he'd record his audio while wearing stilts in order to see the world from Groot's perspective. He said that it was also practice in anticipation of doing Groot's motion capture in any sequels that might happen.
Zoe Saldana had to spend hours getting turned green in order to play Gamora. She said, judging from the strange discharges she kept experiencing, that her body had an adverse reaction to the alcohol-based make-up they were using.
Enforced Method Acting: According to director James Gunn, the translation of Groot's dialogue actually was scripted — but he didn't share it with actors whose characters aren't supposed to be able to understand Groot (i.e. Quill), to get a more genuine response. He did give the translations to Vin Diesel (Groot), and probably also to Bradley Cooper (Rocket).
Executive Meddling: According to James Gunn, Ronan the Accuser was messy because the Marvel Creative Committee was given an input on villains. The group also wanted to nix the now-iconic 70's soundtrack but were thankfully overruled.
Follow the Leader: The success of the movie convinced Marvel's rivals to create their own action-comedy superhero movies with anti-hero protagonists. In 2016, 20th Century Fox released the Deadpool movie and Warner Bros. plans to release Suicide Squad (2016). This goes even extends to the trailers (featuring 70s pop & rock music) and even the release dates (both movies were released in traditional dump months just like Guardians).
I Am Not Shazam: Denarian is Garthan Saal's rank in the Corps, not his first name. Actually made evident in the epilogue when Rhomann Dey was given the same rank as Saal was KIA.
Who would have though that stone-cold badass Vin Diesel would end up playing the gentle-yet-badass Groot? (Outside of those that watched The Iron Giant, of course — which itself was a role where he was Playing Against Type.)
Korath's lack of recognition for "Star-Lord" reflects the obscurity of the comic series compared to other properties from the Marvel Cinematic Universe. His getting it right at the end shows the hope that the film could raise their profile among fans.
Gamora and Rocket's arguments become a bit funnier when you remember that Zoe Saldana and Bradley Cooper are exes.
After appearing in the trailer, "Hooked on a Feeling" by Blue Swede sold more than 2000 downloads within 24 hours of the trailer being released — a 700% increase in sales.
All of the songs that comprised the film's soundtrack, "Awesome Mix Vol. 1", that was released as an album; it became the first film soundtrack to ever hit #1 on the Billboard album charts without a new song debuting on it. It's also worth pointing out that they were heard on radio stations well after the movie premiered.
Howard the Duck's original run was released digitally a week after the movie's launch and a new series early the following year. The success of both is mainly attributed to his cameo in Guardians.
Sleeper Hit: In spite of Marvel's excellent box office record, the movie was expected by most to do relatively modest Thor-level numbers of around $180 million because it was based on a very obscure comic book property and was released in the dump month of August. Guardians of the Galaxy, however, ended up getting the last laugh all the way to the top summer spot, dethroning the presumed summer box office champion Transformers: Age of Extinction, and Captain America: The Winter Soldier as the highest grossing movie of 2014. What made its success shocking was that the previous attempts to make big budget sci-fi space operas in 2011 (Green Lantern) and 2012 (John Carter) were massive bombs. The fact that Guardians of the Galaxy was able to avoid the same horrible fate is a real testament to the success of the Marvel Brand.
So My Kids Can Watch: Djimon Hounsou has admitted in an interview that he took the role of Korath the Pursuer for his son, who loves the Superhero genre.
According to James Gunn, Peter flipping off the Nova Corps came from Chris Pratt goofing around on set.
Chris Pratt also ad-libbed the line "if I had a blacklight, this place would look like a Jackson Pollock painting."
The scene where Peter drops the orb during the Collector scene was also not scripted. According to the commentary, Chris Pratt accidentally dropped the orb during filming but remained in character through the whole thing so it's in the final film.
James Gunn's brother Sean, who did the on-set acting for Rocket, improvised the line "A bunch of jackasses standing in a circle."
Yondu making fun of The Broker by making silly noises was not scripted. Michael Rooker was simply goofing around, feeling that it fit his character and, as the other actors stayed in character, it was kept in. Even Sean Gunn/Kraglin's Corpsing fits.
In 2012, Marvel offered to give Fox an extension on rebooting Daredevil in exchange for the rights to certain cosmic Marvel characters for use in this film; Galactus and Silver Surfer were explicitly named. However, Fox declined the offer.
The song over the opening credits was planned to be "Hooked on a Feeling" but it was decided "Come and Get Your Love" worked better.
Early drafts of the script included Bug. He was even back in the Guardians' comic relaunch to promote the character briefly. He was left out due to his nebulous standing with whether or not Marvel doesn't own the film rights to the character (though he debuted in Micronauts, it was ruled that Marvel's take on Bug was essentially an original character after they lost the rights to the Micronauts).
Early drafts featured Nova (although it's unclear as to which Nova, Richard Rider or Sam Alexander) as a central character. He was cut once James Gunn took over, as he took away focus from Star-Lord's story, as well as being considered The Scrappy by Gunn.
Stan Lee was originally slated to cameo in the Collector's collection on Knowhere, in which he would have flipped off Groot from within a display case (possibly a reference to the fact that Groot is the only member of the team that Lee had any hand in creating). The scene was cut because Lee was in England at the time and couldn't be reached for filming.
Thanos almost got cut from the movie, but Gunn decided to keep him for a connection to The Avengers.
James Gunn wanted to have ROM Space Knight pop up in the movie, but was unable to do so because Marvel does not have the rights to use the character. (It is currently owned by Hasbro after they acquired Parker Brothers.)
Likewise, Nebula was also supposed to die, but James Gunn decided that she should live after filming the deleted scene between her and Gamora mentioned above, in order to provide more story opportunities for potential sequels.
Concept art for Rocket Raccoon and Groot◊ shows that they were originally going to look a LOT creepier.
James Gunn wanted to include aliens called "sneepers". The name ended up being used for the fictional band behind "Guardians Inferno".
In an interview on Jimmy Kimmel Live!, Chris Pratt said that, while filming one scene, he kept saying "pew pew pew" whenever he fired his blasters, because they obviously didn't have any sound effects until they were edited in. This scene had to be reshot to get a take without Pratt's interjections (to the tune of $150,000), although a lot of fans think saying "pew" when he fires his guns would have been perfectly in character for Star-Lord and they should have gone with the original take.