Did I ever tell you what the definition of insanity is? Insanity is doing the exact... same fucking thing... over and over again expecting... shit to change... That. Is. Crazy.

I used to be an adventurer like you … then I took an arrow in the knee.

War.. war never changes.

Do you like hurting people?

Niko, let's go bowling.

But as long as there are people, there will always be war.

Ah shit, here we go again.

There are two kinds of people: ones that are trying to build their future and ones that are trying to rebuild their past.

Tom: Turing tests are tests designed to tell humans and machines apart. Typical problems only solvable by a human. A combination of logical and lateral thinking.
Ava: So you can't complete these tests Tom?
Tom: No. That is why I am glad you are here to help.

You are approached by a frenzied Vault scientist, who yells, "I'm going to put my quantum harmonizer in your photonic resonation chamber!"

I survived because the fire inside me burned brighter than the fire around me.

The last time a big naked dude said he could help me, it did not end well.

Death is a preferable alternative to communism.

I know you think I'm just a mindless recording. I'm programmed to repeat silly bits of patter while you drive around and murder people in this video game, right? Look, maybe that's true. Maybe it's true... but I got a question; how independent are YOU? Turning the tables is what I'm doing here. You think you have free will, but really you're just doing what the game tells you to do. How much control do you really have over your own life? I mean, think about it, this is what you do. Take a look, man... you sit around all day playing a video game and listening to fake radio stations. What are you doing with your life? Don't you want to get a girlfriend and maybe learn something new? Surprise us. Take a class, get a skill... we already know you can punch buttons and pull your pud! C'mon, man!

Cortana: What if you miss?
Master Chief: I won't.