Young Ender Wiggin is recruited by the International Military to lead the fight against the Formics, a genocidal alien race which nearly annihilated the human race in a previous invasion.

Ender Wiggin: In the moment when I truly understand my enemy, understand him well enough to defeat him, then in that very moment I also love him.
Colonel Graff: We won! That's all that matters.
Ender Wiggin: No. The *way* we win matters.
Colonel Graff: You have a habit of upsetting your commander.
Ender Wiggin: I find it hard to respect someone just because they outrank me, sir.
Mazer Rackham: There is no teacher but the enemy. Only he will tell you where you are weak, where he is strong.
Colonel Graff: Tell me why you kept on kicking him. You had already won.
Ender Wiggin: Knocking him down won the first fight. I wanted to win all the next ones, too. So they'd leave me alone.
[last lines]
Ender Wiggin: I need to find out if I'm as gifted at peace as I am at war. They've awarded me the rank of Admiral and left me to my own devices, which suits me fine. I'll travel the universe and carry with me a precious cargo. Because I have a promise to keep.
Ender Wiggin: Sir, you made them hate me
Colonel Graff: I told them you were the best, we need a Julius Caesar, a Napoleon.
Major Gwen Anderson: We were hoping that would be you.
Ender Wiggin: Caesar was assassinated by the people he trusted.
Major Gwen Anderson: And Napoleon lost in the end.
Colonel Graff: Not before he conquered the known world... dismissed!
Bean: [to Bernard] Your mother cheated, that's why you look like a plumber.
Bean: The enemy's gate is down.
[first lines]
Ender Wiggin: Fifty years ago an alien force known as the Formics attacked Earth. Tens of millions died. It was only through the sacrifice of our greatest commander that we avoided total annihilation. We've been preparing for them to come back ever since. The International Fleet decided that the world's smartest children are the planet's best hope. Raised on war games, their decisions are intuitive, decisive, fearless. I am one of those recruits.
Petra Arkanian: At least you don't have any bad habits.
Ender Wiggin: I don't have any good ones either.
Petra Arkanian: I'll give you those.
Colonel Graff: There's only one kid on this launch with any brains at all so far, and that's Ender Wiggin.
Colonel Graff: Let's see how he handles rejection.
Colonel Graff: Don't threaten me boy, I'm not the enemy.
Ender Wiggin: I'm not so sure. I don't want to play this game any more. I quit.
Mazer Rackham: You will have to win this war one battle at a time.
Major Gwen Anderson: After you had already won, why did you continue to hit him? Did you enjoy it?
Ender Wiggin: Knocking him down was the first fight, I wanted to win all the others, so they'd leave me alone.
Bonzo Madrid: Wiggin.
Ender Wiggin: Sir. Ender Wiggen reassigned.
Bonzo Madrid: I asked for a replacement for O'Riley and this is what I get. A useless, skinny, untrained snot. Let me be clear, I intend to trade you a-s-a-p My army has been undefeated for the last 21 battles. I'm trying to get into command school. You can get your training at someone else's expanse.
Bonzo Madrid: Here's the deal snot. When we go into battle, you will not pass through the gates until all my soldiers are through, then you will remain just inside the gate with weapon undrawn and unfired until the game ends.
[Col. Graff is taking Valentine to see Ender]
Valentine Wiggin: Come on. You just want him to re-enlist.
Colonel Graff: I want him to save lives.
Valentine Wiggin: And what about his life?