Kara Danvers wasn't the first Supergirl.
Back in the day, Superman was so popular, there were a number of spinoff comics running at any given time, including titles like Superman's Pal Jimmy Olsen, Superman's Girlfriend Lois Lane, and Superboy. The first female Superman type character was the Lois Lane version of "Superwoman" way back in Action Comics #60. A 1960 Superboy story gave us Claire Kent, aka Super-Sister, after an alien overheard Superboy complaining about women drivers and decided to teach him a lesson with a quick gender-swap. The first proper Super-Girl arrived in Superman #123, via a magic wish from Jimmy Olsen, but that one died saving Superman. Finally, Kara Zol-El arrived in Action Comics #252, via a very convoluted origin story.
Supergirls who almost were.
It's hard to imagine anyone else as TV's Supergirl now, but before Melissa Benoist won the role as National City's most powerful protector, there were of course some other women in the running for the lead. One of them was Claire Holt, who we here at TVWeb absolutely adored on the The Vampire Diaries and its spinoff, The Originals. Other actresses reportedly up for the part at one time or another include British soap star Gemma Aktinson and Elizabeth Lail, aka Anna in Once Upon a Time.
The Glee connection.
Supergirl star Melissa Benoist rose to fame as Marley Rose on Glee. The hit Fox musical dramedy also featured future Flash Grant Gustin and Melissa's real life ex-husband, Blake Jenner, who briefly appeared on Supergirl as Cat Grant's son. In 2017, the CW gave fans a mini-Glee reunion with a two-part musical crossover, where Supergirl and Flash encountered Music Meister, played by Darren Criss.
Of course this isn't the first time Superman's cousin has flown from the comic page to the screen. Most notably, there was the 1984 movie, which starred Helen Slater. In an awesome meta nod, much like former Flash John Wesley Ship playing Barry Allen's dad on The Flash, Slater plays Kara's adoptive mother on Supergirl.
Of course that's not the only super-meta connection on Supergirl. Supergirl's adoptive father, Jeremiah, is played by Dean Cain, best known as one of the stars of Lois & Clark: The New Adventures of Superman, which ran from 1993 to 1997.
But wait, there's more! Erica Durance took over as Supergirl's Kryptonian mom, Alura Zor-El, in 2017. Eagle-eyed super-fans immediately recognized her from Smallville, where she played Lois Lane for six of the show's ten seasons.
A wonderful president
In yet another cool meta nod to longtime DC television fans, Linda Carter showed up in the Arrowverse as the secretly alien President of the United States on Supergirl's Earth. Carter most famously played Wonder Woman on TV in the 70s.
A Super Sister.
Like some of our favorite Arrowverse characters, including John Diggle aka Spartan, Kara's adoptive sister was created specifically for the screen. Alex Danvers didn't originate in the comic books. And we are of course very grateful to the TV series for blessing us with her, as the bond between the two sisters is really the heart of the show. On top of that, she's a kickass character - literally and figuratively.
Maggie Sawyer is in the comics.
Like most of the characters on the show, Alex's true love, Detective Maggie Sawyers, originated on the printed page. She's been a supporting character for both Superman and Batman. In fact, the Metropolis detective was even briefly the Police Commissioner of Gotham and romantically involved with the Kate Kane Batwoman.
Kara died in the comics.
In the famous '80s storyline Crisis on Infinite Earths, which cleaned up and consolidated all sorts of DC multiverse continuity, Supergirl was killed. One of the most famous images in DC history is the Crisis cover featuring a grieving Superman holding his cousin's body. The show even paid homage to this image with this cool promo poster (LINK). Like Superman's own death in the comics, which came about four years later, it didn't last. Kara was kept out of the comics for quite some time before her proper return. There were a few confusing iterations before DC arrived with a Kara Danvers more closely resembling the one we know and love on TV.