protean [ˈproʊtiən] a.
1.) Of or pertaining to Proteus; like that of Proteus; hence, taking or existing in various shapes, variable in form; characterized by variability or variation; variously manifested or expressed; changing, varying.
2.) Zoology. Varying in shape; of or pertaining to the proteus-animalcule; amœboid, amœbiform, proteiform.
3.) Of a theatrical performer: characterized by the ability to take several parts in the same piece; quick-change; also, in transferred sense: of such a performance. Originally U.S.
4.) Of animal behaviour: unpredictable, following no obvious pattern (Oxford English Dictionary 2nd Edition).
Etymology: from Latin Prōteus, adoption of Greek Πρωτεύς: a sea-god, the son of Oceanus and Tethys, fabled to assume various shapes.
"There is one point connected with individual differences which seems to me extremely perplexing: I refer to those genera which have sometimes been called 'protean' or 'polymorphic,' in which the species present an inordinate amount of variation; and hardly two naturalists can agree which forms to rank as species and which as varieties" (On the Origin of Species, Charles Darwin, 1859).