An incubus, much like a succubus, is a demon that visits in a dream or while a person is sleeping. An incubus is the male counterpart to the succubus and shares many of its characteristics, such as visiting a person to have sex with them (since it is male, it only attacks women). According to legends, a woman pregnant after having sex with an incubus gives birth to a stillborn or a deformed child. The legend of the incubus most likely arose to explain the hallucinations seen with sleep paralysis and a pregnancy out of wedlock or from a shameful relationship. During the Renaissance when the culture was less restrained around sex than the Middle ages, there was a rise in cases of young girls giving birth to stillborns without knowing who the father was, resulting in debates to whether an incubus could really impregnate a woman.
The most famous “child” of an incubus is Merlin from the King Arthur legends. Merlin’s mother was a woman of high class but gave birth to Merlin after being attacked by an incubus. She was afraid that Merlin would turn out to be an evil person so she took him to the church to cleanse his body. This left Merlin with only mysterious powers, allowing him to be one of the most famous wizards in fiction.