A metaphysician is a practitioner of the division of philosophy that is concerned with the fundamental nature of reality and being and that includes ontology, cosmology, and often epistemology. To explain further, ontology is a branch of metaphysics concerned with the nature and relations of being, the kinds of things that have existence. Cosmology is a branch of metaphysics, but is also a part of other aspects of natural science, that deals with the nature of the universe, taken as the sum of all that exists as being Real, and how Reality is ordered. Epistemology is the study or a theory of the nature and grounds of knowledge especially with reference to its limits and validity, what can we know and how can we or do we know it.
My Big TOE by Tom Campbell is fundamentally a work of metaphysics.