I is for.....

.......Incubus.


An Incubus is a male spirit that seduces women and mates with them whilst they are sleeping.
It is believed that the magician Merlin was the child of an Incubus, as his mother is said to have never disclosed who his father was.

There are so many tales surrounding the Incubi it is difficult to distinguish facts.  A common thread however is that many of these attacks were blamed on Incubi when in fact they would have been actual rapes by humans.  In medieval times it was easy for the rapist to invent a story and blame it on an Incubus, thus clearing his own name, leaving the poor victim not only feeling even more worthless, but most likely subjected to claims she is crazy too.