Functionalism is the theory of mind which says that mental processes are functions of a brain (or some equivalent). In other words, it says that to understand mind you must view it as a set of functions, or actions, which are carried out by the thinking entity.
Any coherent functionalist theory of mind must also be materialist. That is, it must view mind as a set of functional characteristics of physical brains, advanced computers, or some other equivalent complex organization of matter. Thus from the functionalist point of view there can be no "disembodied minds" or "spirits" of the sort that the gods are often imagined to be.
The most prominent and consistent form of materialist functionalism is DIALECTICAL MATERIALISM.