Are they a lot of Spartans on Halo or is Master Chief the only one? He could be the ''last' Spartan or a rogue one.
I'm not entirely up on the lore, but as I understand it:
Srg. Johnson was part of the Orion program, in hindsight known as the Spartan 1s (that's why he's so badass and doesn't die like other marines).
Chief is one of the last Spartan IIs. I believe Jorge was one.
Carter, Kat, and those from Noble Team in Reach were Spartan IIIs.
All of the above (maybe minus the Spartan 1s, idk) were augmented since about six years old, thus the name, if you know your history, "Spartans."
Spartan IVs (such as palmer and all the people in Halo 4), aren't really the same. They were already trained marines, sometimes ODSTs. Not really true "Spartans" in the since that they were trained and augmented since childhood.
That's why the older smartens are usually bigger and stuff than the newer once. Being augmented since childhood, they were more malleable.
This is also why everybody hates Halsey. She kidnapped little kids to make them into supersoldiers. She thinks she's justified because her work saved the planet.