Who are the gadols / great Torah scholars of today? What determines this? To what extent can they rule on halacha?

I see people like Rab Moshe Feinstein referenced a lot with regards to his rulings.

I see he is referred to and revered as a gadol; who are people on his sort of level today?

What determines someone as being a gadol?

And to what extent can they rule on halacha?

Thank you for any answers