The Supergirl outfit was designed by Colleen Atwood, who also designed the costumes for Arrow (2012) and The Flash (2014). She had previously designed the Superman outfits that would be used in the failed film "Superman Lives" which would star Nicolas Cage in the title role.
In Supergirl: Myriad (2016), Cat Grant says to tell "Harrison Ford she is flattered but she does not date older men, especially when they're married." Calista Flockhart, who plays Cat Grant, is 22 years younger than her husband Harrison Ford.
In late 2014, various reports suggested that this project, planned for CBS, could tie into the shared universe of two other hit superhero shows, Arrow (2012) and The Flash (2014), which air on The CW but are also co-owned by CBS. This was later confirmed, when it was announced in February 2016 that Grant Gustin from The Flash would be appearing in a crossover episode as his character. Later still, in 2016, reports were made of the show moving "properly" to CW for season 2, with further crossovers to be expected.
In an early episode, it is mentioned that Metropolis was destroyed during one of Superman's fights as a nod to Man of Steel (2013). A comic book prequel for that film revealed that Kara Zor-El does exist in that universe.
Blake Jenner, who's portraying Adam Foster (Cat Grant's son and Kara's love interest) in the series, is married to the actress that portrays Kara Zor-El, Melissa Benoist. (Benoist has filed for divorce in December 2016)
The project went through a long and intensive casting process in order to find an actress to play the title character. In January 2015, it was announced that Melissa Benoist had been cast as the lead. Benoist had long been considered a favorite for the role. Other actresses who were considered include Claire Holt, Gemma Atkinson and Elizabeth Lail.
Melissa Benoist read the New 52 "Supergirl" comic in preparation for her role, and reportedly some of them were used in her audition. She was then told by the producers that the TV series would go in a different direction.
Ironically, DC Comics canceled the Supergirl comic book title close to this series' premiere in 2015. It was announced the following year that it would return as part of the "DC: Rebirth" event (as "Supergirl: Rebirth"), incorporating many elements of this series such as the outfit, Supergirl working with the D.E.O., the civilian identity of Kara Danvers, original characters Jeremiah and Eliza Danvers and National City.
Kara and Siobhan Smythe/Silver Banshee become enemies from the moment they meet in this series, while in the "New 52" continuity, they become best friends and later roommates. Siobhan turns out to be the only being on Earth able to understand Kara's Kryptonian speaking due to her Silver Banshee nature, and the first to recognize her as a hero.
According to Brandon Routh on Twitter, the "bulletproof coffee" Cat mentions in the third episode was used by writer Andrew Kreisberg after Routh's "obsessive" use of the term. Routh, of course, played the title character in Superman Returns (2006) and stars as The Atom in Arrow (2012) and its spin-offs.
Initially, while Superman does make brief appearances (played by an uncredited Kevin Caliber) his face is always obscured or off-screen and his voice not heard, with Kal-El only appearing as a child, and the guise of Clark Kent never seen at all (but still communicating with Kara, via text messages). Then, with the show's move from CBS to CW after the first season, it was announced that a 'proper' outing of the character would follow in subsequent seasons with Tyler Hoechlin in the role.
Kara's foster parents are named Jeremiah and Eliza Danvers, a change from the comics in which the Danvers first names were Fred and Edna. In Peter David's run, Linda's parents were Fred and Sylvia Danvers.
Andrew Kreisberg confirmed on Twitter that Kara's ears were pierced when she was still on Krypton. For a brief second, it is possible to see that young Kara's ears are pierced indeed, when she is in her pod.
This is the second time Chyler Leigh has played a character with a name that derives from "Alexander." On Grey's Anatomy (2005) she played Alexandra ""Lexie" Caroline Grey and on Supergirl (2015) she plays Alex Danvers.
Plastino Chemicals and the Otto Binder Bridge in National City are, or course, references to Otto Binder and Al Plastino, co-creators of Kara Zor-El/Supergirl. However, only Superman creators Jerry Siegel and Joe Shuster are credited.
Alex Danvers does not exist in the comics and was created for the series. She notably resembles Linda Danvers/Supergirl, the character created by Peter David after Kara Zor-El was wiped out of comic book continuity.
Live-action debut of DC Comics character Lena Luthor, if not counting the Smallville (2001) character of Tess Mercer, which was an amalgam of Lena, Contessa del Portenza, Mercy Graves and Eve Teschmacher from the Superman (1978) films.
The "alien code" that Wynn is attempting to read in the episode 'Solitude' is the Kryptonian language used in Smallville (2001), the only difference being the characters scroll top to bottom/bottom to top instead of left to right/right to left.
When a picture of Laura Vandervoort from V (2009) was used to make fake ID passports as part of an international identity-theft ring, she was immediately recognized by an FBI agent who happens to be a fan of Smallville (2001) wherein she portrayed Kara Zor-El/Supergirl.
The universe this series is set is designated as Earth-38 as a reference to the year "Action Comics" #1, Superman's first appearance, was published, 1938. In the comics, Earth-38 is a world wherein the heroes (Batman, Superman, Wonder Woman, etc) appeared early in the 30s and aged normally, passing on their legacies to their respective descendants.
While National City was originally created for the show, it first made it's appearance in the comics with Action Comics #51 of the Action Comics New 52 series (after being first mentioned in Batman/Superman #31) when a dying Superman (New 52 version) tracked down Supergirl and found her at the D.E.O. and mistakenly thought she was being held prisoner. National City would be officially shown as Supergirl's home starting with the relaunch of the Supergirl comic book series in the DC Rebirth event not long after.
The fact that Hank Henshaw is Afrcian-American in the show, unlike the comics, as well the design of the cybernetic implants he has on his face, including the faceplate he wore over his cybernetic eye in the episode "Medusa" gives him a closer resemblance to Victor Stone, aka the superhero Cyborg, than his original comic book counterpart.
Tyler Hoechlin reportedly felt difficult to suit up as Superman. "I started to think that Superman's greatest power was actually being able to just jump into [the suit] as quickly as he does, because it's not quite as smooth the first couple of times you do it."
The trivia items below may give away important plot points.
Winn thinks Kara is a lesbian when she is about to reveal her secret identity as Supergirl. In the comics, the Danvers had the same conclusion before their daughter Linda "comes out" as Supergirl to them.
In the comics, the character of Lucy Lane assumed the alter ego of Superwoman (who had a costume bearing a field that simulated Kryptonian powers), and was eventually confronted by Supergirl in the story arc "Who Is Superwoman?". Lucy is one of several characters to take the Superwoman mantle, along with Kristin Wells, Lana Lang and Lois herself.
The Martian Manhunter is friends with Jeremiah Danvers and is granted the mission to protect his daughters Kara and Alex. In Smallville (2001), the opposite happens: the Martian Manhunter is friends with Jor-El and is granted the mission to protect his son Kal-El/Clark on Earth.
Martian Manhunter's human disguise is Hank Henshaw. In the comics, Hank Henshaw is the name belonging to Cyborg Superman, one of the four Supermen to appear after Superman fell in battle with Doomsday.
Chyler Leigh portrayed Dr. Lexie Grey (sister of the title character) who died after an airplane crash in Grey's Anatomy (2005). In this series, she is again the sister of a title character, and is saved by her from perishing in an airplane crash in the Pilot.
Live action debut of several DC Comics characters such as Doctor T.O. Morrow, the White Martians, Miss Martian, Hellgrammite, Red Tornado, James Harper, Mon-El, Draaga, Cameron Chase, Indigo/Brainiac 8 and the Bizarro Supergirl.
In this series, James (Jimmy) Olsen assumes the mantle of the Guardian, a Golden Age vigilante created by Jack Kirby and Joe Simon, also the creators of Marvel's Captain America. In the comics, James Harper is the original Guardian, and does appear in this series as well, in his live-action debut.
Lex and Lena Luthor's mother is Lillian Luthor, a name that was conceived for Smallville (2001). In the comics she was originally named Arlene Luthor, later renamed Letitia Luthor. Lex mentions an aunt named Lillian in "Superwoman" #6.
The Martian Manhunter is an ally of Supergirl in this series. In the comics, the Supergirl known as Matrix, a character created to replace Kara Zor-El, had powers similar to his - shape-shifting, telepathy and telekinesis.