She (sometimes he) is portrayed by Delphine Chanéac.
Dren was created by Elsa and Clive, two scientists who mixed human with multiple animal DNA. She matures fast as she was about six years old after twenty something days. She's at first violent but becomes friendly to the couple, but becomes violent again when she becomes much more mature. Later her molecular structure changes and she becomes a male. She/he then proceeds to kill Clive with the fatal stinger on her tail, but Elsa then kills Dren by crushing her/his head with a rock twice. At the end of the film it is shown that Elsa is pregnant, probably with Dren's child.
When she was born, Dren looked like a deformed creature with no hands but as she matured she started to look more human. As an "adult", she looked like a deformed human with no hair. She has a tail with a tip like a scorpion, webbed feet, mostly black eyes and only four fingers (counting the thumb). Later in the film it is shown she can produce bat-like wings. She has aquatic lungs and needs to be underwater every once in a while. When she became a male she looked a little more disfigured.
Dren couldn't speak but instead made bird-like noises (screeching, cooing, etc.), except at the end of the film when she/he said "Inside You" as she/he was raping Elsa.