Characters with any of the following traits would know this information:
Race: Tiefling, Aasimar
Class: Warlock, Cleric, Wizard
Background: Acolyte, Noble, Sage
Skill Proficiency: History, Arcana, Religion
Experiences: Direct interaction with a Devil through forging a pact
Devils are the creations of Daemaskorn, the God of Contracts, and are the messengers, representatives, and enforcers of Daemaskorn. Devils are widely considered to be "evil", and this is true for the overwhelming majority of Devils. However, there are some that could be better described as "neutral" in that they are not inherently malicious, and instead simply wish to fulfill their role as the foot soldiers or pact-makers of Daemaskorn. While this may come as a surprise to those who interact with one of these fringe Devils, one should remember that despite common belief, Daemaskorn himself is not necessarily "evil", and moreso overwhelmingly spiteful as the God of Punishment and Contracts. That said, one should be exceedingly cautious when interacting with a Devil, as they are quite literally supernaturally crafty by nature. It is their very purpose to tempt or trick mortals into unfavorable contracts for the express purpose of the mortal failing to honor their agreement so that they can be dragged down to the Black Prison realm of Daemaskorn, where they will be subjected to an eternity of torment. Devils will offer all manner of boons in their contracts, as the signing of the contract itself allows them to channel the power of their creator in order to grant said boons, but these contracts nearly unanimously come at a cost that far outweighs the benefits, oftentimes having many hidden requirements that are only revealed to the mortal at a later date when it is more advantageous to the Devil who proposed the pact. While the true form of a Devil is often terrifying and monstrous, many opt to meet a prospective mortal in a much more alluring or disarming guise to ease the mortal's suspicions and assure them that the Devil is there to offer gifts of some kind. Devils are expert liars and can be astoundingly patient, and thus are willing to spend years or even centuries waiting for the opportunity to ensnare as unsuspecting mortal. As such, one should be wary of any Devil that seems to be exceptionally friendly or cooperative, for they very well could have been planning for the exact moment a mortal would interact with them and set up such a situation to disarm the mortal's suspicions. A mortal may "rescue" a Devil from a situation that seemed to be disadvantageous or dangerous to the Devil, being met with overwhelming praise and gratitude in the form of a very tempting contract, realizing only too late (if at all) that the Devil put themselves in a situation where they appeared to require assistance so that they could feign gratitude when a mortal rescues them. It is for this reason that those who study Devils as a species often warn mortals to never take a Devil at face value. It is still unclear, even to those who dedicate their lives to studying these supernatural beings, whether Devils get any direct benefit from dragging individuals to the Black Prison or if they do so simply because it is their purpose. Such information could likely only be gained by visiting the Black Prison yourself, and the list of individuals that have managed to escape from the realm is very short indeed.