A series of video games, books, novels, and other media that is heavily based on the character known as Master Chief. Although there are some games that do not have Master Chief in them, every Halo game currently in existence from 2010 back has referenced him in one way or another. The main enemy in the Halo games are The Covenant, a series of aliens who've come to take over every planet including Earth.
Thomas: "Dude, I'm going to go home and play Reach"
Nicholas: "Reach was okay, but I'm honestly a bigger fan of Halo Wars"
Dario: "You guys are both crazy, Halo 2 was the best of the Saga!"