Guardian Sentinel

The Guardian was a Forerunner Sentinel located at the Ark. They bear a slight resemblance to Compilers from Marathon, a previous Bungie game. They were set to be seen in Halo 3, but were removed, and featured in The Art of Halo 3. They resemble the hologram in the Halo 3 Multiplayer map Epitaph. They are believed to be, or at least are similar to the Guardians of Sandtrap and Sandbox, though no confirmation exists so far.