demons are born out of darkness, there are different kinds, some are good, evil or just neutral, it is possible to make a deal with demons, they normally want your energy or soul as the soul contains power and energy is just power, demons tend to have a different form of power and abilities then us. They have a darker aura then most, there is no true system of ranking between demons, just some are more powerful or weaker, add a comment or email me if I missed something or got something wrong
While I'm no expert on demons I have studied them. Demons aren't evil, like spirits, people, and any other astral being, they can be good or evil, each is different. A demon doesn't always want your soul, but they do want something in exchange for their help, energy for example, and most will get it by any means hence why so many claim they're evil.
everyone has darkness and light, demons are born from darkness just as everyone has, darkness, but everyone has light, so they are born with both, demons are born a bit more demonic then others, that's how they are
Being a demonologist, I think you are mistaken. Demons aren't actuly evil, some are ,but not many. The word demon is derived from Daimon, which has no bad connotations. So at the start, demons weren't actually 'evil'. Demons only became evil when they were introduced into the bible. So some demons can actually be good, but most people don't call them demons because they think that all demons are evil, just the good ones are usually called Daimons. Just a little fact I thought you should know.