Hope Mitchell

is the unsub in episode 2x06 "Cuckoo".

Timeline: 1984 through (at least) January 2009

Location: Dahlgren, Virginia

Age: 35 (born 1974)

Status: gamma (but see below)

Gammanalysis
Crack: Unknown but possibly related to her abusive stepfather

Manifestation: Extreme strength

Victims: Larry Peretti, Stephen Reyes, Dominica Magdziak, Agent Hastings, two EMTs and possibly 196 others (including a federal marshal and an orderly).

Current status: Dead. As of the end of "Cuckoo", she had escaped from an ambulance; a decapitated body that might be hers had been found in a fire in Baltimore, Maryland. Forensics later proved that the body was in fact hers. 

Gamma or Beta?
In episode 3x04 "Spell 81a", Reyes brought up the possibility that she was not in fact a gamma:
 * Reyes cleared his throat. "Actually, she might not have been."


 * Every head at the table swiveled--except Chaz's and Todd's. "Explain, please?" Falkner asked.


 * Reyes licked his lips. "I'm not sure Hope Mitchell was a gamma. I would be inclined to diagnose her as a second-stage beta, comorbid with paranoid schizophrenia. And there's more."


 * Daphne considered screaming when he paused, but he was just taking a breath. And you couldn't blame a man who had been through... that... for steeling himself before choosing to talk about it.


 * "She told me she had known what she was since she was born," Reyes said. "She had some linguistic markers of precocious speech. And... She told me her mother was impregnated by a stranger who came out of a white light. A superhuman stranger."


 * You could have heard a feather drop.


 * Without raising his eyes from the medical reports, Chaz said, "Her father was a gamma."

Speculation
A line of speculation arose on the message boards that "Hope" in the title of episode 4x04 "Hope is Stronger than Love" might refer to Hope Mitchell. Naturally, the Powers That Be steadfastly declined to confirm or deny the possibility.