You basically just described Halo's precursors except they actually are immortal even if killed they can choose and take a new form. Also they are older then the universe by around 86 billion years.
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But the precursors were wiped out by forerunners right? Sorry I haven't gone deep into the forerunners
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They where but only because the Precursors where so in awe of one their creations destructive power. Also they choose to uphold the mantle and not fight back. But they have died many times and they come back they can choose corporal forms or none corporal forms so they can come back as flesh and blood or as basically spirits.