Noble Six, or Spartan-B312, was one of the greatest Spartans to ever live. He was a member of the Spartan III program's Beta Company, and an ONI headhunter. After the death of the original Noble Six, Thom-A293, he was transferred to Noble Team, stationed on Reach. Shortly after he was integrated into the team, the Covenant attacked Reach. During the month-long campaign against the Covenant, most of Noble Team would be killed, save for Jun-A226. During Noble Six's last mission, he delivered the AI Cortana to the shipbreaking yards of Aszod, which hid the cruiser Pillar of Autumn, carrying John-117, the Master Chief, before the ship fled Reach and ended up at Installation 04 days later. During the mission, Noble Six and Emile-A239 were the only Spartans from Noble Team left on Reach, with Jun having been sent on a different mission that ended up saving his life. Tragically, Emile was killed during the mission. After the Pillar of Autumn left, Noble Six held a position near the boneyard for hours before an entire Covenant battalion was sent to finally kill him. It is not known whether or not he survived, and many speculate that he survived anywhere from six weeks to six months, either dying to Covenant hunting parties or being glassed by a Covenant ship from orbit, while many more speculate that Noble Six is still alive. He was one of only two Spartans to ever be designated hyperlethal, with the other being the Master Chief.
Originally, I said that Emile and Six were the only Spartans left on Reach during the delivery run to the Autumn, but that is not true. Multiple other Spartan III fireteams were active on the planet as well, and so were over half of the remaining Spartan IIs, most of whom were killed during or after the final conflicts on the surface.