This is Stan's grandfather (full name: Marvin Marsh). He's old, dying and is constantly trying to kill himself. He helped lead the AARP in their charge to not take old people's licenses away. He is also an elite member of the Hare Club For Men.
Season 1: Cartman's Mom Is a Dirty Slut
The boys decide to submit their video of Cartman to "America's Stupidest Home Videos."