An intelligent character pretends to be less intelligent in order to fool people about how effective they are. In many cases, a character pulling this off may play along until they're in a good position to drop the charade and get serious, usually catching anyone underestimating them badly off-guard. Another variant of this, primarily found in teen comedies, is the popular student (almost invariably a girl) who acts like The Ditz in order to avoid being stigmatized as a nerd.