Part of that expansion was explaining the UNSC's Spartan program and the soldiers that inhabit it. There are four different generations of Spartans with the Spartan-IIs being considered the strongest.

Spartan-III Program The Human-Covenant war was going badly for humanity, and Spartan-II's were extremely expensive and time-consuming to produce.

1 John-117 The man, the myth, the legend. Master Chief, John-117, is the face of the franchise, the game's box art, and the face of the Spartan Program as a whole.