'The Flash" Showrunner Breaks Down the Evolution of Killer Frost

Killer Frost returned last night on The Flash and while Caitlin Snow's cold side made only a brief appearance there was a lot revealed about the character's history. Now, showrunner Todd Helbing is breaking it all down.

Last night, Caitlin (Danielle Panabaker) was reunited with her father Dr. Thomas Snow (Kyle Secor), but their reunion wasn't precisely a happy one. Caitlin learned that her father had created a cryogenic treatment to cure himself of ALS as well as that she herself had the genetic markers for the disease, so he treated her with the treatment as well. The result was the creation of the icy alternate personality Killer Frost and while initially Thomas played it off that he was without a frosty dual self and was, instead, dying of a "cryogenic malignancy" it turned out that the Thomas Snow Caitlin found was more a look at what could have been Caitlin's fate with Killer Frost.

You see, Thomas did have a frozen alter ego, Icicle, who had been in charge for so long that Thomas' human side barely even exists. He was trying to manipulate Caitlin into giving him a serum that would allow him to erase the human Thomas for good. Fortunately for Team Flash, Killer Frost returned suddenly during a confrontation with Icicle stopping him before he could erase Thomas and kill the heroes. It was that sudden return that helped the team realize that it The Thinker didn't absorb Caitlin's powers last season. He simply put a mental block in place and, with the use of Harry's mental dampener, Caitlin can communicate with Killer Frost and eventually bring her back.

It's a huge shift for Caitlin and Killer Frost, one that Helbing said changes things going forward (via EW).

"In previous seasons, her becoming Killer Frost was always motivated by some emotional response, but we wanted to sort of move in a direction where it became more symbiotic, where she could call upon Killer Frost whenever she needed her or sometimes just to talk," Helbing said.

Executive producer Eric Wallace noted the impact on their communication as well.

"They don't have to pass notes anymore," Wallace said. "They can actually speak to one another."

This ability to speak with Killer Frost directly will have more impact than just the ability to get icy on demand, too. It will help Caitlin truly know herself and make huge strides towards fulfilling her own destiny.

"She gets to learn about this whole side of herself and her childhood," Helbing said. "That's like having a twin who you didn't know about and then comes back into your life, and you're able to learn things about yourself that you'd never know."

It's something that Panabaker herself told ComicBook.com is very important for Caitlin.

"I think it's going to be really important," Panabaker said. "You know, toward the end of the season we saw Caitlin try to understand a little bit more of why she disappeared... so I think also this year she's uncovering some mysteries about Killer Frost and how Killer Frost came to be and we're going to see her delve into that."

The Flash airs Tuesdays at 8 p.m. ET on The CW.