Gnosticism
Gnosticism refers to a collection of early Christian off-shoots that believed…several different things.
Because I haven’t looked into Gnosticism extensively, this will be very brief and…maybe a little incorrect. I’ll find out once I do look into it a bit more.
Gnosticism essentially believes that there are two gods. The god that created the world and then the actual God. The god that created the world is either evil or incompetent. By the way, his name is sometimes Yaldabaoth, though he’s also sometimes just called the Demiurge.
The purpose of existing is to escape the material world to enter the Pleroma. This is achieved by attaining Gnosis – hidden knowledge.
The bad god doesn’t want you to attain Gnosis, which is one of the many reasons he’s an annoying prick (according to the Gnostics.
Gnosticism has the distinction of sounding like it was crafted by an actual demon, which is hilarious on the one hand. Also, hearing Gnostic interpretations of the Bible is deeply amusing.
Gnosticism also has a figure called Sophia who…I don’t really fully understand, but she’s usually the reason the bad god exists in the first place. Also, she might be the female analog of Christ.
The only surviving Gnostic tradition that is actually definitely Gnostic is Mandaeism. I find Mandeism to be interesting in another very important way: from the very little that I’ve seen, it isn’t nearly as cynical as most forms of Gnosticism are.
There are a few Gnostic revivals that exist, though I know nothing about them. Something I am aware of though are the Gnostic fanboys. These are people (usually of a New Atheist inclination) who really really like defending Gnosticism, and making out its destruction as a tragedy. More may be written on them separately.