Ron Weasley, Harry Potter, Hermione Granger and Neville Longbottom
In 'Harry Potter and the Deathly Hallows, Part 2,' we finally return to Hogwarts with Harry (Dan Radcliffe), Ron (Rupert Grint) and Hermione (Emma Watson), as they attempt to find and destroy the last horcruxes (bits of You Know Who's soul) necessary to defeat Lord Voldemort once and for all.

Upon arriving at their beloved wizarding school, the Trio reunites with their old schoolmates and friends, who've banded together to reconstitute Dumbledore's Army (the D.A.) in resistance to the new Death Eater–led administration (now led by Headmaster Severus Snape). Here's a Who's Who of the major D.A. members who have a much more significant presence in the final Potter installment than the previous, Trio-centric 'Deathly Hallows, Part 1.' (Mild spoilers ahead.)

Neville LongbottomNeville Longbottom
Who He Is: Harry and Ron's painfully shy Gryffindor mate, Neville (played by Matthew Lewis) is a herbology genius who's usually a klutz (he and Hermione were the last to learn how to fly) but has a valiant heart. Neville has fought alongside the Trio at every turn, and we last saw him standing up to a Death Eater on the Hogwarts Express.
Why He's Important: Neville ran the D.A. in Harry's absence, keeping up morale (even after being tortured by the sadistic new Dark Arts professors) and using the Room of Requirement as the resistance movement's secret headquarters.
Did You Know: He has good reason to hate Voldemort -- his Order of the Phoenix parents were tortured to the point of insanity by Death Eater Bellatrix Lestrange.
Scene-Stealing Moment: Bloodied and wounded, he gives an awesome climactic speech and wields Gryffindor's sword with the bravery befitting his Hogwarts house. The important sword "presents itself to any worthy Gryffindor" in his time of need, in this case killing a particularly evil creature.

Evanna Lynch as Luna LovegoodLuna Lovegood
Who She Is: Considered an oddball, this ethereal Ravenclaw(played by Evanna Lynch) believes in all sorts of mythical creatures and legends, but she's extremely kind and honest -- and always has her friends' backs. We last saw her helping to bury Dobby at Shell Cottage after being kept prisoner at Malfoy Manor.
Why She's Important: Luna answers Neville's call to return to Hogwarts once the Trio arrives. Her kindness to all creatures helps Harry track down one of the last horcruxes.
Did You Know: Luna is the only non-Gryffindor in Harry's inner circle of friends, and her Ravenclaw affiliation means that despite how "loony" she might seem, she's actually quite a brilliant witch.
Scene-Stealing Moment: She's gotten used to friends dismissing her fanciful ideas, so her forcefulness with Harry when she tells him why he needs to go speak to a certain ghost is particularly surprising and effective.

Oliver and James Phelps as Fred and George WeasleyFred and George Weasley
Who They Are: Two of Ron Weasley's five older brothers, the twins(played by James and Oliver Phelps) are best known for playing elaborate pranks, which eventually leads them to start their own joke shop. Despite their newfound fortune, the twins always volunteer for missions to aid the Order and Harry.
Why They're Important: The Weasleys treat Harry like part of the family, so it's no surprise the twins join the ultimate battle. Like everyone who fights that night, they put their lives on the line to help their favorite "speccy git."
Did You Know: Fred and George are the second twins in their family to raise their wands against Voldemort. Their uncles Fabian and Gideon were former Order of the Phoenix members who died dueling five Death Eaters in the First Wizarding War.
Scene-Stealing Moment: As is to be expected from the Weasley twins, they have a memorable, funny exchange right before the Death Eaters and their army descend upon Hogwarts.

Bonnie Wright as Ginny WeasleyGinny Weasley
Who She Is: The youngest child (and only daughter) in the Weasley clan, Ginny (played by Bonnie Wright) is Harry's love interest / best friend's baby sister. A fierce witch, Ginny's a stellar quidditch player and a natural at defense against the dark arts. We last saw her sitting next to Neville on the train to Hogwarts.
Why She's Important: She's a Weasley, all of whom take up arms against Voldemort in the climactic battle, and she's Harry girl. Ginny even points her wand at Bellatrix Lestrange until her mother Molly intervenes.
Did You Know: That Harry-Ginny smooch you've seen in trailers is not in the final book. The only couple that manages to snog during the Battle of Hogwarts is -- you know it -- Ron and Hermione. So Harry-Ginny fans get a bonus kiss on-screen.
Scene-Stealing Moment: When she first sees the Trio has returned to Hogwarts, she only has eyes for Harry -- despite the fact she also hasn't seen her brother Ron or close pal Hermione in months. Her star-crossed response leads to one of Ron's signature one-liners.

Battle at Hogwarts in Deathly Hallows Part II
The Order of the Phoenix
Who They Are: They're the surviving members of a secret society started by Albus Dumbledore to oppose Voldemort. Those who remain include former auror Kingsley Shacklebolt (George Harris); new parents Remus Lupin (David Thewlis) and Nymphadora Tonks (Natalia Tena); Molly (Julie Walters) and Arthur Weasley (Mark Williams); newlyweds Bill Weasley (Domhnall Gleeson) and Fleur Delacour (Clémence Poésy); Aberforth Dumbledore (Ciarán Hinds); and Professor Minerva McGonagall (Maggie Smith).
Why They're Important: They're the most skilled and experienced wizards on Harry's side (in addition to the various professors) during the Battle, since the majority who fight are current and former Hogwarts students.
Scene-Stealing Moments: All of them show impressive fighting skills during the Battle, especially expert-at-defense Kingsley, who effortlessly fells every baddie who heads his way; Professor McGonagall, who commands a stone army to protect the castle; and the surprisingly good dueler Molly Weasley, who protects her children with the ferocity of an angry lioness.