Here come the good guys.
The Order of the Phoenix is a top-secret group that Dumbledore established during the First Wizarding War to fight off Voldemort and his Death Eater henchmen. Now that Voldy is back, the old gang is getting back together, too.
Let's do call role:
Remus Lupin (David Thewlis): Harry's old Defense Against the Dark Arts teacher (and werewolf by full moon) is obviously a member of the Order. Remus explains to Harry that the Minister of Magic has it in for him. He also shows up at the Battle of the Department of Mysteries.
Severus Snape (Alan Rickman): Harry's pretty surprised that Snape is in the Order. Can we actually trust this guy? Snape also spends part of the year trying to teach Harry Occlumency, but that doesn't go so well. Harry also learns some uncomfortable truths when he delves into Snape's memories… like the fact that his dad might have been a bully. Oh, no.
Rubeus Hagrid (Robbie Coltrane): Hagrid is away for most of this movie when Dumbledore sends him on a journey to recruit giants to join the Order of the Phoenix. Is Hagrid successful? Maybe. He definitely succeeds in bringing home his half-brother and all-giant, Grawp.
Arthur Weasley (Mark Williams): Ron's dad is wounded by Voldemort's snake while on patrol as a member of the Order. Luckily, he's saved by the mystical visions of Mr. Harry Potter.
Molly Weasley (Julie Waters): Ron's mom is super-maternal in this movie. She pushes hard to keep Harry in dark about the goings-on of the Order. After all, he is just a boy. What could go wrong?
Alastor "Mad-Eye" Moody (Brendan Gleeson): This is actually the first time Harry meets his Defense Against the Dark Arts teacher from last year (considering that he spent the entire events of Goblet of Fire locked in a trunk). He's also pretty hardcore.
Kingsley Shacklebolt (George Harris): Kingsley works for the Minister of Magic which gives him an in to what's happening in the wizard government. Nothing good, we assume.
Nymphadora Tonks (Natalia Tena): Tonks is an Auror who can change her appearance at will. It's cool. Just don't call her Nymphadora.
Minerva McGonagall (Maggie Smith): It's never explicitly stated in the film, but obviously Professor McGonagall is a member of the Order. She's totally Dumbledore's woman through and through.
Arabella Figg (Kathyrn Hunter): Harry's neighbor Mrs. Figg might be a Squibb, but she's Dumbledore's eyes and ears on Privet Drive.
Alice & Frank Longbottom: Neville's parents are original members of the Order of the Phoenix who were tortured into insanity by Bellatrix Lestrange. They actually didn't die, so we think that means they're still in the Order. Honorary members for life?
Phew. That's a lot of people fighting the good fight. They're probably going to finish Voldemort off by the next movie. What? There's three more after this one? Come on, guys—you're gonna need to up your game.