I only have seen a few episodes of Spongebob, but Patrick Star is the dumbest character I have seen on television. Before him I would argue Hooterville's county agent had an I.Q. of a lima bean and wonder how he could get the position let alone keep it even among the dimwitted citizens of Hooterville. Dating Ralph Monroe doesnt help either. He is not a cartoon character granted I think of him every time dumbest television characters comes up. At least Homer has the crayon excuse, but not this guy.
https://en.m.wikipedia.org/wiki/Hank_Kimball