The first draft of the script the villain was supposed to be John Harrison, renegade Starfleet officer turned terrorist. Then Orci or Lindelof (I forget which) had the idea "what if John Harrison was an alias and he's really Khan?" Which ever one thought it up, the other was against it, and the two spent an entire year arguing over it, which is why the movie's release was postponed from 2012 to 2013. When the decision was made to go with Khan, they decided to use John Ericson as the alias, as an easter egg, and thus all the actors spoke that name while filming. But during post-production, Orci worried this made it way too obvious to the fans that the character was Khan and thus had it dubbed to Harrison.