In Islam, Djinn are a creation, just as people and angels are. People were created from earth, angels from light and Djinn from fire. People have freedom of choice (as do Djinn, whom can be good and bad and from any faith) whereas angels can only obey the commands of God, hence there is no "fallen angel" in Islam.

The Dajjal has great explanation in Islam, I could write a book about it. It is said his name will be Abdulla son of Cyatid and that he will appear between Syria and Iraq and be of Jewish descent. I am not sure if he will be born but have not found any evidence he is Djinn.

One website gives his physical description, as narrated in various hadiths as "He will be blind in one eye, while his other will be like a "floating grape". He will be short, fat, hen-toed, crooked-legged, with black curly, woolly hair, and a ruddy complexion. He will have on his forehead, between his eyes, the word "kaffir", which any believer, literate or illiterate, can read"

I fond all of this extremely intersting, as you may tell :)

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"Diplomacy is the art of saying 'Nice doggie' until you can find a rock - Will Rogers"