Forerunner Cavalier

The Promethean Cavalier is a deleted Promethean construct that was intended to be introduced in Halo 5: Guardians. The Cavalier was apparently intended to start out as an empty shell, which would then be filled by the Cavlier itself. The Cavalier was intended to use a Forerunner polearm weapon and was capable of shielding itself. It's possible that due to similarities in abilities and appearance, the Cavalier design eventually became the basis for Warden Eternal.