The Raven Mocker, or ka'lanu ahkyeli'ski is an evil being from Cherokee mythology who robs the old, sick and dying of the lives. Normally appearing as old withered men and women, when they hunt a victim they take to the air in a fiery shape, and with the sounds of a raven's cry and a strong wind. After tormenting and killing their victim by slitting on the victim's head they consume his heart (doing so without leaving a mark on the victim's skin). This is said to add another year to their life for every year that the slain would have still lived.
Much like the Banshee, the sound of a Raven Mocker means that someone will die soon. Raven mockers are normally invisible when feeding, but those with strong medicine can not only spot them but cause them to die within seven days. Medicine men will sometimes stand guard over the dying to prevent raven mockers from stealing the heart of the afflicted.
Raven mockers are feared and envied by the other witches of Cherokee folklore, and their bodies may be abused by said witches after death. He is the Angel of Death in such a way he was menacing.
There are tons of books about Raven Mockers that are all revolving around such a scenario.