Who's Killer Frost?

Who's This? A cold-hearted lover.

The facts: Killer Frost first appears in Firestorm #3 (June 1978), created by Gerry Conway (RIP) and Al Milgrom. She is Crystal Whitney Frost, a student of Martin Stein's who crushed on him, but was rebuffed. She becomes a scientist and while working on a project in the Arctic, an accident turns her into a psychotic killer with the power to project cold. She naturally goes after Stein and therefore, Firestorm. She dies in The Fury of Firestorm #21 (see below), but her friend Louise Lincoln later reproduces the accident and tries to avenge Crystal. Lincoln, fairly indistinguishable from the original, would be Killer Frost's identity until the New52, which introduced a new KF, Caitlin Snow, which will sound familiar to Arrowverse fans. Though Louise Lincoln scored an appearance in World's Finest most recently, she hasn't properly been seen since the Doomsday Clock event.
How you could have heard of her: Television's Caitlin Snow was a scientist played by Danielle Panabaker on The Flash, so we knew she was destined to become Killer Frost at some point. Versions of Killer Frost also appeared in the DCAU, Batman: The Brave and the Bold, and Young Justice. In DC Rebirth, Snow became the default Killer Frost, and was rehabilitated as a member of the JLA (as, simply, Frost).
Example story: The Fury of Firestorm #21 (March 1984) "Cold Snap!" by Gerry Conway, Rafael Kayanan and Rodin Rodriguez

Selected because both Crystal and Louise are in it - though the latter doesn't become Killer Frost yet - the original KF's last story has the future KF telling her she's dying. Under the "ice sheath" of her skin, her body is deteriorating, with - at most! - days to go. In her anger, Killer Frost smashes a console in Louise's lab, which sets off an alarm. Louise cowers, afraid her old school friend will take it out on her, and she might, but doesn't go further than calling her mediocre (academically) and "eager to please" (with men) before three armed guards rush in to get killed.

Oh, it's comics and one can survive being quickly frozen? Not if Killer Frost smashes your ice sculpture, which she totally does.

Louise's horrified reaction makes me wonder why she would ever want to become Killer Frost herself, but for now, the OG walks out on the Jersey Turnpike, causing icy mayhem, sure to lure Firestorm to her location. He's been looking for her since she attacked Stein in the previous issue, and when he sees fires burning in Jersey, he ignores them because Killer Frost has to be his priority. Well... So eventually catches up to the readers and while he can solve some of the pile-up's problems with his powers, she's long gone. He follows her ice trail, which leads to Louise Lincoln, from which he learns that Frost is ill, and could do anything if she has nothing to lose. Back on the Hudson River, she's icing up ships and kissing sailors to steal their warmth. And by now, her "ice sheath" has started to come down.

Firestorm shows up. They fight. He tries to contain her. She throws sharp icicles at him, but eventually traps him in the ice.

Psycho near-ex or not, Professor Stein at least wants to save her. He counsels Firestorm to try and freeze her until a cure can be found, but she destroys his giant hair dryer and even manages to wound Firestorm!

But if what she wants is to steal Firestorm's warmth, maybe it's time he just gave it to her. It could heal her. It could destroy her. We'll see how much is inside the Nuclear Man.

In the end, she completely evaporates. Oops! And a depleted Firestorm knocks at Lorraine Reilly (Firehawk)'s door and passes out.

But you can't keep what is arguably Firestorm's greatest villain (what? Multiplex?! Are you kidding?) down, and she would return. An ice villain might have been able to "reform" after this event, and it's probably how *I* would have handled it. She returns, sans flesh, just ice, more insane than ever. Instead, they minted Louise Lincoln as the new (identical-looking) Killer Frost. It's an odd choice, honestly, and maybe why she CAN'T be given the greatest villain award. So who... Plastique?

Who's Next? Batgirl's original nemesis.