Since its debut in 2014, The Flash has been a mainstay of The CW's lineup of shows based on DC Comics superheroes. Starring Grant Gustin as the titular Scarlet Speedster, the show is now on its way to securing a ninth season, which would make it the longest-running Arrowverse series on the network. Learn more about DC's "Fastest Man Alive" with these Flash facts.

1. The Flash and Supergirl both starred in Glee.

From the moment The CW announced its musical crossover episode between The Flash and Supergirl in 2017, fans were intrigued to see which stars from the two shows would break out into song and who would actually be able to carry a tune. However, fans of Fox’s Glee knew right away that the two leads from both shows would be able to deliver big.

Both Gustin and Melissa Benoist (who plays Supergirl) starred in the Fox musical comedy, setting up a mini Glee reunion when they joined forces for the memorable crossover. But the Glee connection didn’t end with Benoist and Gustin. Actor Darren Criss, who was cast as Music Meister (a.k.a. the villain at the heart of the event), co-starred alongside both Benoist and Gustin on Glee, where he played Blaine Anderson for five seasons.

2. The Flash’s Robbie Amell is cousins with the Green Arrow.

Actor Robbie Amell, who starred as Robbie Raymond throughout the early seasons of The Flash, is the younger cousin of Stephen Amell who played Oliver Queen, a.k.a. the Green Arrow, on The CW’s Arrow. While Robbie and Stephen Amell’s relationship is one that most fans are familiar with, Robbie’s family connection goes a bit deeper than many recognize. In addition to being related to the man responsible for launching the Arrowverse, Robbie is married to actress Italia Ricci, who played Siobhan Smythe on Supergirl.

3. A number of actors from the '90 Flash series are in it.

The CW has always featured cameos from past DC stars in its new-era shows, and The Flash is no different. The biggest connection to the past comes in the form of John Wesley Shipp, who played Barry Allen in 1990’s one-and-done Flash series. In the CW version of the show, Shipp plays Barry’s father, Henry Allen. Then there's Mark Hamill, who played the Trickster in both the original ’90s series and the current iteration of the show. Finally, Amanda Pays reprised her role as MERCURY Labs scientist Amanda Pays from the original series.

4. Grant Gustin almost played a love interest to Thea Queen.

If there is one thing that CW viewers know, it’s that the network is keen on recycling talent across several shows. Not only did Grant Gustin appear on the network’s 90210 revival, but he nearly was cast during the first season of Arrow as a love interest for one of the show’s leading ladies. In an interview with BuzzFeed, CW casting director David Rapaport revealed that Gustin had auditioned for the role of Thea’s boyfriend during the first season of Arrow but was ultimately passed over.

"How screwed would I have been if we cast him then?!?," Rapaport later joked.

5. Matt Barr and James Mackay almost played The Flash.

It’s impossible to imagine anyone other than Gustin playing the role of Barry Allen. However, the role could have just as easily gone to Matt Barr or James Mackay, who were both in contention for the role.

6. IMDb nearly ruined Zoom’s identity.

After actor Teddy Sears was cast in The Flash, IMDb credited the actor as playing both Jay Garrick and Zoom on the show long before the big reveal was made that the Jay Garrick first introduced on the show was actually Earth-2’s evil speedster Zoom. Had it not been for the quick action of executive producer and writer Andrew Kreisberg—who learned of the crediting from Sears—season 2’s biggest mystery would have been spoiled long before the big reveal was made. Luckily, the error was remedied within a number of days.

7. Don’t bother looking for Eddie, Harrison, or Tess in the DC Comics.

With every comic book series, the writers have a wealth of characters to pull from in deciding who to bring into the fold. However, sometimes the best thing a superhero show can do is introduce its own original characters, which is precisely what The Flash team did with the likes of Eddie Thawne, Harrison Wells, and Tess Morgan.

The trio of characters never appeared in the DC Comics and the characters were created specifically for the show. While the roles of Tess and Eddie were minor in comparison, it’s impossible to imagine the show without Harrison Wells, who has been a crucial part of The Flash since the first season.

8. Emily Bett Rickards is responsible for Grant Gustin’s casting.

The CW team could not have found a better person to play Barry Allen than Gustin. And his casting was the direct result of the chemistry he shared with Arrow actress Emily Bett Rickards, who plays Felicity Smoak.

As revealed in a bonus feature for the show’s DVD set, the casting director felt that it was crucial for Barry to have good chemistry with Felicity as she would play an integral role in introducing the character to viewers. Because Felicity was so loved by viewers, it was believed that if she loved Barry, viewers would, too.

9. The Flash led to a Prison Break revival.

Years after Prison Break wrapped its four-season run on Fox, co-stars Wentworth Miller and Dominic Purcell reunited on The Flash in the roles of Leonard Snart (a.k.a. Captain Cold) and Mick Rory (a.k.a. Heat Wave). It was the Prison Break reunion fans had been hoping for, and working together on The Flash is what ultimately led to conversations about bringing the mid-2000s Fox series back.

“We hadn’t seen each other in about five years,” Miller told to the members of media in attendance at Fox’s 2017 Television Critics Association winter press tour. “Suddenly we were back on set, discussing old times. And out of that conversation came the possibility of revisiting Prison Break.”

Had Miller and Purcell not teamed up on The Flash, Fox’s Prison Break revival, which ran in the spring of 2017, may not have ever occurred.

10. The police station mural holds a secret Justice League Easter egg.

If you pay close attention to the show, you’ll notice that within the Central City police department is an oversized mural of notable figures from Greek mythology.

To the naked eye, the mural seems like nothing more than an artistic piece to give the department some style. However, those mythological figures were specifically chosen to represent the various heroes of the Justice League, including Hermes (Flash), Zeus (Superman), Hades (Batman), Hera (Wonder Woman), Apollo (Green Arrow), and Poseidon (Aquaman).

"I wanted to do a deco [themed] set and [the sculpting style of] bas-relief in the deco era was rampant and so was the Greek mythology in their sculptures," Flash production designer Tyler Harron told Entertainment Tonight. "So I said I'd like to put in an Easter egg that represents [each] one of the Justice League members."