Elektra Natchios, more commonly known only by her first name, Elektra, is a character in the Marvel comics. She is of Greek descent and has a few back histories that at times conflict, but usually her history involves the death of a loved one and Elektra's desire to gain revenge because of that death. In some universes, Elektra is a student in the present day and attends university, where she meets Matt Murdock, who becomes her love interest and is also the hero Daredevil.
Elektra is one of the fiercest and most able female characters in all of comics, not just Marvel, but also DC comics. In an alternate comic, several fighters from Marvel go up against several fighters from DC comics, and Elektra is able to win against Catwoman, although she decides not to defeat her and instead only damages her whip. Elektra is strong, capable in both body strength and mind, and it is thought that she has mind abilities that surpass the normal human being's.
The character of Elektra first appeared in 1981, in a Daredevil comic book, but since then has her own comics. Elektra has also been included in a Daredevil movie and in her own movie, in which she was portrayed by Jennifer Garner. More information about Elektra will be included soon; for now please visit her detailed page on Wikipedia.
As a side note, I was thinking about naming the fanlisting several names, including Kunoichi, or female ninja, or Haunted, because Elektra is haunted by events in her life, no matter what universe is telling her story.