Who are these people?

[pasithea]

postvixen, magnavixen, and prickvixen

I see their names as response posts in almost all of the journals of people I have on my friends lists but I have NO idea who they are. All three seem pretty cool (which is surprising given they're all vixens) so I have to wonder who they are before my noggin starts coming up with ideas like they are really the internet equivalent of the three furies of greek mythos or something.