The succubi are depicted as feminine demons who haunt the dreams of men. They seduce men in their sleep and (less often) even when these men are conscious. According to "Malleus Maleficarum" (1486), they were after the semen of men. Either to use it for magical uses, or to ensure the births of more demon. More recent interpretations depict them as vampiric creatures who feed on the souls and/or life forces of men.
Their male counterparts are the incubi. Both of these sex-related kinds of demon were considered to have a corrupting effect on their mates. Inspiring their mortal lovers to embrace sin and sexual vices. The embrace of the succubus has been connected to sleep paralysis, exhaustion, and death.