Kalona is a fallen immortal brought back to life by Neferet. In his past life, he was known for wreaking havoc and hurting women. Kalona has the ability to transform his appearance and appears beautiful to anyone who looks at him. Specifically, he has large black wings and golden eyes.
In the book Hidden he reveals that he is actually the brother of Erebus, who later appears twice in the novel wanting Kalona to leave the House of Night alone, each time the two make snide comments and jabs at one another. In the same book he is shown unable to walk into Nyx's temple.