Technically, Elektra's another character who first appeared in a comic in late 1980, as she first appears in DAREDEVIL #168, dated January 1981. A miss being as good as a mile, though...
Her creator Frank Miller has freely admitted that he patterned Elektra on Will Eisner's lady thief Sand Saref, right down to having his male hero pursue the way of law and justice while his former girlfriend pursued illegal thrills. However, given that the late 1970s began the slow transformation of many juvenile-aimed superhero comics into what I've termed Adult Pulp, Elektra was designed to be a much darker figure than Eisner's jaunty lady thief.
Like Daredevil himself, Elektra's origins are informed by "father issues," in that the death of her father depresses and disillusions her to the extent that her practice of the martial arts is also corrupted. She falls in with one of the baddest of the bad crowds, a sect of murderous ninjas called the Hand. Though in time she breaks away from their order, from them she learns the discipline of being an assassin-- in which identity she falls afoul of Daredevil, a.k.a. her former lover Matt Murdock.
The continuing altercations of Elektra and Daredevil-- as well as other continuing villains Bullseye and Kingpin-- transformed the DAREDEVIL title into a dark tapestry of brutality and sadism, with a few touches of Freudian-themed sex in the mix as well. Finally, in the DAREDEVIL title at least, Elektra transcended the pollution in her soul. However, Miller did not leave the character alone, last reviving for the 1990 graphic novel ELEKTRA LIVES AGAIN.
For some time, Marvel kept the Elektra character sequestered from most of the Marvel universe, apparently in the anticipation that Miller might choose to come back and sell more Elektra books. Eventually, when Miller did not return, Marvel began farming out the character to other raconteurs, much to Miller's dismay.