It is the creator, a super race that first inhabited the newly formed universe after Big Bang. Now this is the last of their ancient race and he must have some special soft spot towards humanity, perhaps we were his most perfect creation of all the life he seeded and now, as we are besieged he rushed to aid us , nearly at the cost of his own life or perhaps it actually cost him his life. That might be the reason for the sphere just hovering above the Last City. It was his last stand, and now it has become his tomb. A testament to an ancient race, who's sole intent was to populate the galaxy and fill them with all various forms of life imaginable.