There's nothing in the world quite like advice from a grandparent. Sometimes it's helpful and sometimes it's the bridge into about five or six different stories, but more often than not, the words of the elderly are heartfelt.
At least that's the way it was with Grandpa Phil on Hey Arnold! He was as full of war stories and senile ramblings as he was with great advice, but he's always been hard to resist as a stable supporting member of the show. And even in his old age, he's willing to mess up some Nazis. That's determination.
He's the whole package as a grandparent and he's got plenty of fantastic moments to spare throughout the series. Just...don't forget to wash your hands.