Antediluvian Conquest of our Planet by Aliens in Flying Saucers

Read about the most fantastic legend ever told a certain battalion of alien creatures once visited earth in the remote past, who after metamorphosing their bodies into human shape started mingling with mankind and begun generic fertilization experiments between themselves humans and animals, which resulted in producing a plethora of legendary giants and mythical monsters who terrorised humanity. Later they decided to destroy them using super weapons and flying machines which resulted in triggering the Genesis deluge, thus forcing them to their origial abode. Who were these alien creatures? Where did they come from? What was the purpose of their visit? Will they someday return? Are some of them still amongst us?