Eliza Harker is an original character from a universe where everything you ever read in Dracula is true - except the happy ending didn't stay happy for long.
Vampires are real. And so, too, are vampire hunters. The most notable group of vampire hunters, owing chiefly to their history (though also for other reason), would be the Harker family; Eliza is the youngest surviving daughter of the line. We say "surviving" because she had to kill her only sister, Stephanie, to prevent Stephanie from becoming a vampire. Family keeps you dead when living is worse, after all.
Her great-grandfather, Quincy Harker I, is the current leader of the most prominent vampire organization; he calls himself the Red King and claims to be Dracula reborn. He has a tendency to try and kill his family for the sake of something to do. (Also for other reasons, but they don't know that.)
He has, currently, nearly succeeded in his efforts; Eliza's father was decapitated and his head placed as a welcome-home gift on her bed, and the rest of the Harker clan have scattered to the four winds.
She's kind of fucked in the head. The Nexus isn't helping much.
She's also played by Todd. Which should really explain everything.
