1901, in the biological sense, from Latin mutantem (nominative mutans) "changing," present participle of mutare "to change" (see mutable). In the science fiction sense, it is attested from 1954. As an adjective from 1903.
mutant mu·tant (myōōt'nt)
An organism possessing one or more genes that have undergone mutation. adj.
Resulting from or undergoing mutation.
A weird and disgusting person; shpos: Marvin is a mutant; he's constantly licking his nose in public (1980s+ Student)