Sunday is Monkey Covers day here at YACB. Because there's nothing better than a comic with a monkey on the cover!
Brainiac 5 is becoming a gorilla on the cover of Adventure Comics #330 (1965) by Curt Swan and George Klein.
(Standard disclaimer about shape-changing teen-age super-heroes not really being monkeys applies.)
Image courtesy of the GCD. Click on the image for a larger version.