An incubus (plural: incubi) is an evil fairy or Demon in many cultures. They take the form of a handsome man in front of a woman in order to seduce her. They whisper nightmares in people's ears to instill a sense of chaos, fear and terror.
The legendary wizard Merlin is the son of a woman and an incubus. Incubi are represented as being cruel and twisted men, with reptilian wings and tails. The female counterpart is a succubus (plural succubi). Incubi are sometimes associated with dark magic and the devil. Incubi, like vampires, are blinded by the sun and are nocturnal.
In addition, incubi sometimes sire children with women.