The identities of main characters in the HALO saga are kept a secret because BUNGIE thought it would make audiences "HOOKED". EG. The Master Cheif,(HALO COMBAT EVOLVED, HALO 2, HALO 3) Sierra 117's identity is kept a secret because if the Spartons identity was known, the game would'nt be so good. EG. The Rookie, (HALO ODST) Again his identity is a secret because he is the main character and he is the games LONER. EG. NOBLE 6 (LONE WOLF)( HALO REACH) Another secret identity for the games story and again you could say it HOOKS you into playing it. Every HALO game that has been and will get made will have a character with a secret identity. It's just how BUNGIE likes it.