The spartan 2 came first. The spartan 3 came after the spartan 2s. The spartan 3s technically never were introduced in the game, just in books. Also, only one spartan 3 survived Onyx.
No only change your color.
It's rated R for nudity (a sex scene and a topless Oracle of Delphi) and, of course, violence.
The Spartans were from the city of Sparta in the province of Laconia on the South Eastern part of the Peloponnesus Peninsula of Southern Greece.
The Spartans were the military of the city-state of Sparta.