Board Thread:Questions and Answers/@comment-104.172.189.120-20150505044206/@comment-29819477-20160827083554

Ghoul mythology comes from Arabs actually who describe ghouls sort of an "evil genie", they were said to be grave robbers who consumes human flesh.

Now if we go by original stories, you don't become one but you are being born as one. They believed ghouls to be hybrids of devil mixing themselves with humans and as such giving offspring of ghoul. Now other three interesting things about ghouls from myths is that they are stated to look exactly as humans but if they don't feed regularly they will take more monstrous and deformed look as well lose grasp of their sanity and humanity, also they can take form of person they have devoured as well and also they are said to be able to shapeshift into animal forms, using mostly the form of animal such as hyena in here.

It is all I know regarding the myth known as ghouls at least.