According to the book of Genesis, these creatures (Nephilim) were present before & after the Global Flood. Nephilim means “Fallen Ones” which are the product of Fallen Angels (Dimensional Entities) and man. Nephilim can be giants, or an array of other (sometimes even Monstrous) humanoid beings. Nephilim are literally creatures genetically made from man.
Every culture on Earth (particularly the Darkest & most occultic) have records of summoning Entities in ~ the Entities in these texts and legends ALWAYS have a sexual interest, most commonly these records (such as in our Earliest Civilizations of Egypt & Sumeria) will include the production of part man / part “god” offspring following the summoning of such beings.