Void is surprisingly useful.

I think it's not really a type at all; it's a keyword used in places in type declarations where an optional type parameter isn't used. While "int *" is "pointer to int", "void *" isn't "pointer to void", it's just "pointer". "int (*)(int)" is "function that takes int and returns int", but "void (*)(int)" is "function that takes int and calling it is a statement rather than an expression", and "int (*)(void)" is "function that returns int". Subsequent language design research showed that optional type parameters are a bad idea, and you can make your parameterized types uniform by including some types that the compiler optimizes (like having "function that returns a value you must discard" instead), but that's not how C was designed, so void ends up with all the weirdness that you get if you try to have a value that embodies the effects of not using something optional.