From Halopedia, the Halo wiki

A fan-made image of Mister Chief created for use in Template:Realworld.
This article contains information about a non-canonical subject that, while official, is not part of the established Halo universe.
A render by Bungie employee Paul Russel.

The Thorax was an ambient lifeform intended to inhabit Installation 04 in Halo: Combat Evolved. Mostly blue, with luminous yellow on its back, it had thin arms but long, powerful legs and a single eye. It was cut from the final game.[1]