D&D Monsters: Succubi

The word "succubus" comes from Latin, referring to a type of demon that seduces men and slowly saps them of their vitality over a series of sexual encounters. This basic concept, however, long precedes even the Romans, with the general idea of  'evil demonic seductress' being fairly common across many cultures. It may, in part, be connected with the same sort of hypnogogic phenomenon that is responsible for the night hag myth - albeit interpreted in a more pleasurable manner. Indeed, succubi were not originally regarded as being attractive in their natural form - although, as with the D&D creature, they could shape-shift - the 'sexy' form only starting to become the standard in modern times.

D&D Monsters: Devils

In regular English, the term 'devil', when not applied specifically to Satan, is essentially synonymous with 'demon'. Whereas the word 'demon' originally had a more benign meaning, 'devil' has always meant an evil entity, and now typically means one that is specifically part of the Christian mythos even if the general concept exists in other religions, too. 

In D&D, however, devils are distinct from demons, making up the organised legions of Hell rather than being rampaging creatures of malevolent chaos. In 1E, six main types exist, although other common ones have been added since, all fitting within a defined hierarchy where weaker devils can (with difficulty) be promoted to higher ranks at the whims of those even higher up the chain. Compared with the demons, these six standard types are more likely to owe their origins to myth or at least to traditional depictions of such beings, rather than just being odd combinations of animal parts. 

D&D Monsters: Erinyes

The Erinyes originate in Greek myth, where they are goddesses of vengeance cursing kinslayers, oathbreakers, and the like; they are probably better known under their Roman name of "Furies". These original versions appeared as ugly women, typically with snakes entwined in their hair and wrapped around their bodies and limbs. Sometimes they had wings, sometimes not, and later depictions of them are similarly varied.

Some versions of the myths state that there are only three Erinyes, but others are much vaguer about the numbers. Notably, the three named Erinyes stand guard over the City of Dis surrounding the Sixth Circle of Hell in Dante's Inferno. It may be this that inspired their adoption as a type of "devil" in D&D, although they (and Dis) are moved to the Second Circle in the 1E Monster Manual, befitting their status as the weakest of the true devils in that edition. Something of a demotion from their mythic origins, then.

D&D Monsters: Demons

Given that "demon" is such a broad term in real-world mythology and religion, there are inevitably many different interpretations and forms of the beings. They were included in D&D right from 0E, where they are listed simply by a numbered type, increasing in power from one to six. Alternative names are provided in 1E, which become the standard names from 2E onwards. Notably, 2E also tried to pretend that they weren't really "demons", lest that offend anyone religious, and described them instead using the invented word tanar'ri. 3E switched back to "demon" again, explaining that the "tanar'ri" were merely a common subtype; the latter term has largely been deprecated since. 5E restored the numbered type sequence, but only as rarely-used categories of increasing power so that, for example, chasme mosquito-demons are now another example of Type 2 demons, alongside the original hezrou.

D&D Monsters: Vrocks

The word "demon" comes from Ancient Greek where it was used to describe semi-divine beings and generally lacked the negative connotations of the modern word. Early Christians later co-opted it as a term for "servitors of foreign/hostile deities", from which it rapidly morphed into something more explicitly evil. In that sense, it's a common concept in many real-world religions, a generic term not linked to any one in particular and that therefore fits with the typically polytheistic worldview of D&D.

The vrock specifically has no direct antecedents in mythology or in Christian demonology. It may be partly inspired by the demonic Tash from C.S. Lewis's Narnia books, but the resemblance isn't that strong and could be coincidental. Vultures appear in the myths of both African and American cultures since similar birds live on both continents. (In reality, the "vultures" on either side of the Atlantic are not closely related, despite their physical similarity, but this may not be relevant in a fantasy world).