Dr. Caitlin Snow/Killer Frost
Dr. Caitlin Snow is a bioengineering expert and a crucial part of Barry Allen's S.T.A.R. Labs support team.
During that fateful explosion at S.T.A.R. Labs she lost her fiancé, Ronnie Raymond. At least that is what she believes when she meets Barry Allen. The character is described as the ice to Ronnie's fire, foreshadowing their future metahuman abilities from the comics.
Caitlin: Ronnie's alive. I saw him Cisco. I think he was following me...
Cisco: Caitlin, Ronnie died. He was vaporized in the accelerator when it went critical.
Caitlin: Ronnie's alive and he's out there, alone and scared and I need your help to find him.
Caitlin: Since when do we have facial recognition software?
Felicity: Happy Hanakuah.