The typical player characters in the Halo franchise.
They are space marinesupersoldiers created by the United Nations Space Command, candidates are given extensive genetic and physical augmentations, and, starting from the second generation, their iconic MJOLNIR powered armor.
In-universe, the project initially started to create an elite force to quell a growing insurrection against the UNSC. Initial candidates were adult volunteers, but the first phase of the project was considered a failure. Eventually, under the lead of Dr. Catherine Halsey, the second generation would be approved, infamously seeing to the abduction of several dozen children from across human space. These children would be indoctrinated and given much more extensive and invasive augmentations and would be deployed just in time for the Human-Covenant War.
The SPARTAN-IIs would be the most famous and successful generation, eventually being supplemented by the cheaper SPARTAN III program, making use of war orphans and using them as "fire-and-forget" weapons in one-off high-risk operations that resulted in high casualties. After the war's conclusion, the program would come full circle and the SPARTAN-IVs would consist of adult volunteers undergoing a more refined augmentation process.
