Halfrek or Hallie is a recurring fictional character on the television series Buffy the Vampire Slayer.

In the season 5 episode "Fool For Love", Halfrek uses the persona of Cecily while on a job to kill all the guests at a party Spike is attending.

(Cecily's surname was implied to be Underwood in the episode "Lies My Parents Told Me", but stated to be Addams in the script and credits of "Fool for Love" and the non-canon tie-in novel These Our Actors.)

The timing of this event would indicate that Halfrek existed as a demon at least three decades prior to the adoption of the youthful human form in Cecily.

She seems to have had at least some pity for William in spite of her rejection of him, as the night he became a vampire, she caused the deaths of the rude party-goers who had laughed at his poetry.

Continuity-wise, the comic story takes place in Buffy season 6, and assumes that Spike briefly left Sunnydale and visited Los Angeles.