By James Hibberd
September 16, 2014 at 01:00 PM EDT

Everything about The Flash happened fast. Producers conceived of the spin-off just two months after Arrow premiered. They cast the first actor who auditioned to star. And now The Flash will debut on The CW on Oct. 7, just two years later, as one of fall’s most anticipated shows. The birth of TV’s fastest man alive was one of the fastest spin-offs ever made, and if you give us a couple quick minutes we’ll tell you just how it happened.

Creating: December, 2012, executive producers Greg Berlanti and Andrew Kreisberg were hard at work on the first season of Arrow, when Berlanti had an idea: Flash spin-off. Kreisberg recalls replying: “We just got our hands on this one!’” But The CW’s entertainment president Mark Pedowitz was on the same page. “They delivered on Arrow pretty quickly and the Flash is a DC character that never got his full due.” Plus, while Flash exists in the Arrow universe, the character had a creative bonus their buff bowman lacked — super-powers. Yet to pull off a spin-off, the producers needed perfect—

Casting: The plan was to introduce The Flash (aka Barry Allen) on an Arrow arc, but “if we don’t cast him correctly it would have been like transplanting a bad organ into the body,” Berlanti says. Finding a star seemed infinitely harder than casting his predecessor. “We already have one show where we have a square jawed, prototypical, muscle bound hero,” Kreisberg explains, so for Flash they needed an actor who could be light, funny, attractive, likable, yet with “pain behind his eyes” and still carry a series AND convincingly beat up hulking bad guys. Enter Grant Gustin (Glee) who was the first to audition, then “echoed throughout the entire casting process and never left our minds,” Kreisberg says. Gustin’s tactic was to not play Allen remotely like a tough hero. “I just tried to be a real guy, really bright, and just leave it at that—let all the superhero stuff come later.” With Flash cast, they turned to the—

Writing: — which was going to be unusual, too. The Flash has a three-episode roll-out (two introducing the character on Arrow last season, then one traditional pilot for the fall.) On the first day in the writers’ room after the pilot was ordered, the staff filled up six dry erase boards in a brainstorming session of all the cool stuff they wanted to see The Flash do. “We literally have hundreds and hundreds of crazy ideas for us to draw from,” Kreisberg says. Yet The Flash was beaten to the pop culture punch on a few of those tricks when X-Men: Days of Future Past premiered this summer with a similar character, Quicksilver, stealing the show with his speedy antics. “Everybody was emailing each other over that opening weekend, but more from a place of that we felt like we were onto something,” Berlanti says. And the core of Flash’s powers were, of course, to show the character—

Running: The Flash runs way faster than a speeding bullet. The trick is to convincingly show him sprinting around Central City, along with plenty of other super powers, without looking cheesy (there’s about 200 effects shots in every episode). “We have whole floor of artists working around the clock.  If it looks like it could be on the ’90s version of the show, we have to do better,” Berlanti says. For Gustin — who quit soccer as a kid because he hated running — it means wearing The Flash’s super-hot red leather suit with a mask glued to his face (“I start sweating pretty much as soon as we put it on,” he says). Gustin often sprints on a treadmill that’s cranked up to 9.0 while hooked into a safety harness against a green screen. “It’s actually still too slow — I’ll over exaggerate my upper body, like really speed up and not take normal steps,” he says. That down, producers turned to—

Shooting: Villains like Captain Cold, General Eiling and Reverse Flash will appear soon, and there’s an Arrow cross-over in episode 4. But expect Allen’s romantic life to develop more slowly, especially his crush on Iris West (Candice Patton). “That relationship I think is going to be a really slow burn,” Gustin says. Likewise, producers plan a gradual rollout of The Flash’s powers. A few will be hit within the first few episodes — like running up the side of a building. Others — like time travel, running on water, and passing through solid matter — are part of the full-series plan. The producers compare Allen to an athlete learning his limits and note that gradual discovery is part of the fun. Still, don’t expect them to wait too long. “I think we have to get to stuff faster probably than we otherwise would have,” Kreisberg sighs. “Everybody is telling the story a lot faster on TV now.”