Halo’s Spartan-IIs are the class of supersoldiers that exist in the same time frame as John-117, aka Master Chief. Created by Dr. Catherine Halsey, the S-II program began in 2525 to combat the Insurrectionist movement. The conscripts were young children kidnapped at the ages of 5 and 6 years old, with short life term clones inserted to replace them into their families.
This program was the first in the series to put its soldiers under biological augmentation, which killed 30 of the 75 children and crippled 12 others. Their last names were replaced with service tags to marginalize their old civilian lives. As of Halo 5, there are five Spartan-IIs still in known active duty: Master Chief, Frederick-104, Kelly-087, Linda-058, and Naomi-010 (who doesn’t make an appearance in the game).