War Hero

From Halopedia, the Halo wiki

War Hero is an achievement in Halo: The Master Chief Collection. It is unlocked by completing all campaigns on Heroic difficulty. The achievement is worth 40 gamerscore. Despite the achievement description, it does not require the completion of the campaigns of Halo: Reach or Halo 3: ODST, because the achievement was created at the initial release of the collection, at the time of which the two games were not yet added to the collection.