A metaphysician.
Philosophers sometimes say that metaphysics is the study of the ultimate nature of the universe.
The branch of philosophy which studies fundamental principles intended to describe or explain all that is, and which are not themselves explained by anything more fundamental; the study of first principles; the study of being insofar as it is being (Latin: ens in quantum ens).
The view or theory of a particular philosopher or school of thinkers concerning the first principles which describe or explain all that is.
The metalogic of physics; the logical framework of physics.
The study of a supersensual realm or of phenomena which transcend the physical world.
Displeasingly abstruse, complex material on any subject.
Any fundamental principles or rules.