Conan McNulty is a former wrestler. He is also the grandfather of the McNulty boys. Conan is frequently portrayed as being Grandpa Lou's most pronounced rival, like most of Lou's rivals he is normally seen lying or cheating in anything.
It is revealed that he has been cheating in the episode, "Wrestling Grandpa" where at the moment he celebrates his victory after his rival, Lou "Pretzel Maker" Pickles forfeits the match at the Wrestling Match Senior Division, a can of motor oil falls out of his costume, and Lou discovers that he has been cheating the whole time during the match, and announces it with the evidence. As a result, he is disqualified.