1997 (real world)

1997 is the year Halo started development.

Prior to September 24

 * Halo started development under the initial codename "Armor".

September
September 24
 * The trademark for Halo's first codename "Armor" was filed.

After September 24

 * Bungie worried that "Armor" was boring and changed Halo's codename to "Monkey Nuts", knowing it had to be changed later.