Ellie (2005)

Ellie is a half-breed demon that was in a relationship, with  John Constantine. She was the one, who informed, John, that Lucifer, would come up, and personally collect his soul, when the time comes. She's one of the many demons, who sides, with Mammon, her reasoning behind this, was that she preferred being on Earth, and Mammon's reign would ensure her place there. John, with the help of Chas, was able to defeat the demons, but John was unable to kill, Ellie, so he let her go.

Ellie was portrayed by Michelle Monaghan in Constantine, although all of her scenes were deleted in the final version of the movie thus eliminating the character from the official canon of the  movie universe.