A Jinn (pl. Jinni), or "Genie" most likely is the same creature as the Roman Genius (pl. Genii); who, like their Greek counterparts, the Daimones are said to have been the members of a noble race, installed as leaders over the first people of the Golden age.
Cronos (Saturnus, Cernunnos) was aware of the fact that no human being is capable of having irresponsible control of all human affairs without becoming filled with pride and injustice; so, pondering this fact, he then appointed as kings and rulers for our cities, not men, but beings of a race that was nobler and more divine, namely, Daimones. Plato, Laws 713a
An inscription from Beth Fasi'el near Palmyra pays tribute to the "Ginnaye", the "good and rewarding gods" providing a sharp resemblance to the Latin Genius and Juno: The Guardian Angels, or Watchers mentioned in 1 Enoch.
In this book it is told that, while most Watchers remained Holy; Guardian angels, others fell and became known as Fallen Watchers or; Demons.
Iblis; Ha Bel Az; the lord Az, or; Azazel is called a Jinn in the Koran.
And indeed, We created (physical) man from sounding clay of altered black smooth mud. And the jinn, We created aforetime from the smokeless flame of fire. (smokeless = pure; originally they were good angels. Flame of fire is the Spirit of God.) And (remember) when your Lord said to the angels: "I am going to create a man from sounding clay of altered black smooth mud. "So, when I have fashioned him completely and breathed into him the soul (Jeeva-Atma; soul posessing Atma or Neshama) which I created for him, then fall (you) down prostrating yourselves unto him." So, the angels prostrated themselves, all of them together. Except Iblīs (Satan), - he refused to be among the prostrators. (Allāh) said: "O Iblīs (Satan)! What is your reason for not being among the prostrators?" [Iblīs (Satan)] said: "I am not the one to prostrate myself to a human being, whom You created from sounding clay of altered black smooth mud." (Allāh) said: "Then, get out from here, for verily, you are Rajīm (an outcast or a cursed one)." [Tafsīr At-Tabarī] "And verily, the curse shall be upon you till the Day of Recompense (i.e. the Day of Resurrection)." [Iblīs (Satan)] said: "O my Lord! Give me then respite till the Day they (the dead) will be resurrected." Allāh said: "Then, verily, you are of those reprieved, "Till the Day of the time appointed." [Iblīs (Satan)] said: "O my Lord! Because you misled me, I shall indeed adorn the path of error for them (mankind) on the earth, and I shall mislead them all. "Except Your chosen, (guided) slaves among them." (Allāh) said: "This is the Way which will lead straight to Me." "Certainly, you shall have no authority over My slaves, except those who follow you of the Ghāwīn (Mushrikūn and those who go astray, criminals, polytheists, and evil-doers, etc.). Qur'an - Ar-Rahmaan 55:15, 15
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Ibn Abdul Barr said, "The jinn, according to the scholars of the language, are of different types:
In several verses in Old Arabic and Old Persian Bible translations, the words: Jinn (جن) Jaann (الجان) Majnoon (مجنون) and Iblis (ابلیس) are mentioned as translations of familiar spirit or אוב(obe) for Jaann and the devil or δαιμόνιον daimonion for Iblis.
Types of Djinn include the ghul (night shade, which can change shape), the sila (which cannot change shape), the Ifrit and Marid. According to the information in The Arabian Nights, Marid seem to be the strongest form of Djinn, followed by Ifrit, and then the rest of the Djinn forms.
All this is about devils, satans, or demons; souls gone evil.
A soul may live in a body like all of us do, or may be without a body, like the deceased do.
If a soul of a deceased person has a strong enough spirit; the Holy Spirit of God living in him, he may ascend to Paradise.
If a soul of a deceased person has a lack of Holy Spirit, he needs to go back to Earth and reincarnate in order to gain more Spirit by learning and experiencing life. He will though, loose his conscient memory of his passed life.
If a soul refuses to "go to the Light" and risks being sent back as another personality, it might stay here on the earthly plane, where it eventually will grow weaker and weaker unless it is able to feed itself on energies emitted by human souls. Without bodies these demons or Jinni may try to make a dwelling in Places with a history, or in living peoples bodies , where they will feed on the negative energies they prefer. They will do so by trying to induce their victims to sinful activities, or by simply taking over this body all together by possession. Souls may become more and more persistent to be "Bad" and gradually turn into demons, whether in, out of, or without a body.
In the end all souls, demon or not, will pass through fire where only the ones blessed with Holy Spirit will be able to reach Paradise. Up till then, demons who will not better their lives, will hardly choose to go through there and remain stuck in their own self-created hell.