Not overly smart but not really stupid either. Personality wise he tends to be sort of goofy and semi humorous. Originally he was more sulky and sometimes he does go into depression a bit due to his past.
TV version is, to quote Stick, a thundering dumbass.
CB version is clever, likely above average intelligence, and def. street smart, but not a genius or anything. Probably half a dozen to a dozen IQ points lower than the likes of Bruce Banner or Reed Richards.