Lolita is full of doubles, also knows as doppelgängers: Humbert and Quilty, Annabel and Lolita. (Even the name "Humbert Humbert" reflects an in inner duality.) In spite of Humbert's deep resentment of Quilty, he cannot help but admire the playwright's verbal skills. Quilty is the one person in the novel whose intelligence Humbert even remotely respects. They are bound by their perverse desire for Lolita. That Quilty follows Humbert around the United States emphasizes the sense that Quilty is a shadow figure to Humbert.
Still, Humbert and Quilty have more in common that even Humbert would like to admit. To Humbert, Quilty is the evil one, the depraved one, praying on Lolita. When Humbert finally confronts Quilty in the end, he announces that Lolita was his child, as though he has played a role of concerned parent and protector. In a sense, then, killing Quilty is Humbert's way of doing himself in since he knows he will go to jail where he belongs. As they fight in the end, their bodies blend together, as Humbert describes the scene: "We rolled over me. They rolled over him. We rolled over us" (2.35.55). Between Humbert and Quilty, there is a constant switching back and forth between who is the hunter and who is the hunted. They are also both "enchanted hunters" of Lolita because they are both mesmerized by her as they prey on her.
As for the Annabel and Lolita doubling, Humbert sees Lolita as Annabel's reincarnation and the cure to his life-long ache over losing Annabel. Most importantly, they are both nymphets.