Ender Wiggin

Ender wears a monitor on the back of his neck, and the military sees everything he sees. At school, Stilson and his gang corner him. Ender wins, then keeps hitting until the other boy can't fight back, so no one tries again. At home, his brother Peter threatens him; his sister Valentine protects him.

Colonel Graff sees what he was looking for in that fight. He removes the monitor, visits the Wiggins and invites Ender to Battle School. Ender says yes to get away from Peter, even though it means leaving Valentine.

On the trip up, Graff praises Ender in front of everyone. It's on purpose: the other cadets start to hate him. In the zero-g Battle Room, Ender realizes that "the enemy's gate is down" and rethinks how the fight works.

Assigned to Bonzo Madrid's Salamander Army, he's banned from fighting. Petra Arkanian trains him in secret. In one match Ender disobeys orders and wins the game, and Bonzo's grudge grows.

Graff gives Ender his own team, Dragon Army, made of rookies and rejects like Bean. Ender invents new tactics every match and wins even when the rules are rigged against him.

Bonzo corners him in the bathroom. Ender fights to end the threat, and Bonzo is badly hurt. Shaken, Ender asks out and goes back to Earth. Only a talk with Valentine by a lake convinces him to return.

At a forward base near the Formic home world, Ender meets Mazer Rackham, the hero of the first war, whom everyone believed dead. With his Dragon Army friends commanding the squadrons, he faces harder and harder simulations.

In the final test, Ender sacrifices most of the fleet and fires the MD Device at the planet. Only afterward does he learn the battles were real and that he wiped out an entire species. He finds the last Formic queen, who gives him an egg. Ender takes it into space, looking for a world where her kind can start over. He still carries the guilt, but now with a purpose: giving the species he destroyed the chance it never got.

In the book, Ender is 6 when he goes to Battle School and 11 when the war ends. The film keeps him around 12 the whole way through and drops Peter and Valentine's online personas.