Comix (which are typically understood as distinct from comics in that they intend a mature audience) got their start in the 1960s. Our earliest evidence of the word comix used as a generic term dates to 1969, but it had begun appearing in the titles of specific works a little earlier than that: one example is the title of R. Crumb's highly influential Zap Comix, first published in 1968. The kind of alteration that changed "comics" to "comix" isn't a 20th century phenomenon: the word pox, as in "chicken pox," began as "pocks" but has been spelled with an "x" since around 1475. A similar kind of alteration, though in this case going from a simpler spelling to a less intuitive one, is the word phat, which is most likely a variation of "fat." "Phat" dates to 1963.