An incubus is a demon that enters the dreams of woman and engages in sexual activity in order to have a child. It is classified as a male counterpart of the female succubus, who engaged in sexual activity with men. Like the succubi, incubi wore out their partners with constant sex and would even kill them.
The Incubus is just as beautiful and desired as his female counter part the succubus.
The origin of this sex demon takes place in Mesopotamia, where the first incubus, Lilu, existed. Lilu is a male counterpart of Lilith, who was a succubus.
Lilu (the counter part of Lilith) was the only other one who matched her sexual appetite and vengeance on the children of Adam and Eve for the sting of betrayal.
The incubus and succubus are actually the same. They swap genders at specific points. For example, they would become succubi whenever they required semen, their life source. They would then become incubi and use that semen to impregnate women. Many believe that incubi are bisexual but that would strictly contradict their purpose of impregnation. But some people believe that when the Incubi slept with another male he would absorb his seed and use it as his own.
When a human has intercourse with a succubi/incubi over long amounts of time (say a month) they will start feeling a need for more sex with the incubi/succubi or go insane from how much life force they have lost.
Sometimes, these demons are able conceive children. When they do, they will obtain supernatural abilities and can become extremely persuasive. These human/incubi or succubi hybrid is called a Cambion. Unless the Incubus slept with a succubus then the succubi would give birth to a new incubi or succubi.
In Islam and Arabian folklore incubus is known as Hadun الحضون Al-Hadun lit. incubator) and Kaboos (Arabic: الكابوس Al-Kabūs, lit. incubus "colloquial for bad-dreams") only difference with Judeo-Christian incubi is being a type or a class of the jinn.