In the Halo series, which era of SPARTAN is Master Chief?

In the Halo series, Master Chief is a SPARTAN-II. The SPARTAN-II program was the first generation of supersoldiers created by the United Nations Space Command to combat rebellions and the threat of the alien Covenant. Master Chief, also known as John-117, was among the group of exceptional children who were abducted at a young age and underwent intense military training and bioaugmentation to become enhanced warriors. The SPARTAN-II program represents the era of Spartan that Master Chief belongs to because of their advanced combat skills, unmatched physical prowess, and iconic armor design, making them the most legendary and iconic Spartans in the Halo universe.