Grandpa Pat, as he was called by the young Eliza, suffered from a declining mental state before the Great War, particularly after his wife passed. It got to the point that he became a burden on his family with his constant rants about the government and pestering other family members about the security of the farm. Fears of a government shutdown or takeover were not alleviated by the hefty insurance taken out on the farm, and the situation only grew worse with time, even after grandpa moved in with the rest of the Gibbons family.
When the Great War hit, the family took shelter in the bunker at their island. However, poor sealing and damaged hazmat suits resulted in the protection failing. The entire family was turned into feral ghouls, with old Patrick becoming a particularly nasty form: A glowing one.