Living Stars is the conjectural name for the species which TBS and Eclipse belong to, originating from the Forest of Lights. They are so ancient, their real name was lost to time itself. They have taken it upon themselves to become the guardians of reality from their own dimensional plane, although some of them have rebelled against this ancient tradition and actively work to cause chaos, such as Eclipse.
Living Stars are extremely temporally acute, and have the power to appear anywhere in space at will, as well as change their size and heat. Some of them also recruited lost souls to aid them in their goals and gave them elemental powers - these became the Time Guardians. Upon meeting potential new Time Guardian recruits, Living Stars do their salute, which involves putting one of their fists in their mouth and lighting it with fire, which makes their bodies glow twice as bright.
As of today, the Living Stars have not been seen in action anywhere in the multiverse for several years, and their Time Guardians are now scattered and without purpose. This is a troubling prospect which demands an explanation, yet has not received one.