Vin
No Longer Homeless!
Fancy Pants
Posts: 9,843
They're a handful of guys from the Order of the Phoenix. The Order was established by Dumbledore the first time Voldemort attempted to rise to power, and since his return has been reformed. They have to operate in secret however, due to the current Ministry's stance on You-Know-Who.
The Dementors, incidentally, attacked Harry under Umbrige's orders.
Nymphadora Tonks, distant cousin to Sirius Black, is a metamorphmagus, which means she can change her appearance at will. She recently finished training to be an Auror (a dark wizard catcher), and has joined the Order of the Phoenix.
Sirius is Harry's godfather, and was Harry's father's best friend. He was framed for the murder of over a dozen people, sent to Azkaban, and then broke out and attempted to commit one of the murders he was committed for. He's not a "bad guy," although he can be a bit reckless which is why Hermione and Mrs Weasley don't think the best of him. And Snape absolutely loathes him, due to events when they went to Hogwarts together.
Well, while I think the first two Harry Potter books are intended for children, the others were written for a much wider audience. And while they're certainly not genius literature, they do have great stories and create a great world, of which the movies are a shallow representation.