'Guardians'? Mendicant Bias, Locke, Arbiter

As we know these ‘Guardians’ are coming. My question is who these ‘Guardians’ are? I’m certain Mendicant Bias will be one, as 'Guardians will probably refer to some class of A.I. On another hand, ‘Guardians’ could refer to the heroes of H5, Namely Chief, Locke and the Arbiter. Can anyone think of what would best fit the title of ‘Guardian’?

The forerunners?! I mean the iso didact or the librarian.

[frumentarii] terminology ‘Guardian’ referencing signal borders [protract] [magnus] parameters… further analysis required…
Feasible tangent suggestion… unseen overseers of the galaxy [sagittarius]…

I personally think the forerunners would be the Guardians, but not 100% sure.

You were killed by the guardians…
The guardians are fate it’s self.

An enemy far more powerful than the forerunners.

in some halo’s if you drown it says killed by the guardians