Green Lantern Vol 2 #18.  Silver Age Hal gets a lot of shit for being denser than a collapsing star.  But consider this: He was still clever enough to outsmart Sinestro.  Multiple times.  This is the man who in modern comics is hinted if not outright stated to be the Greatest Green Lantern.  Here, he has been imprisoned in amber by an Earthling who smacked his head on things so often it became a defining character trait.