It turns out that Waylon Smithers Sr., much like his son, was the right hand man to the evil, conniving Charles Montgomery Burns, tyrannical owner of Springfield's nuclear power plant. It also turns out that he died a hero, saving the town, and his newborn son, from radiation poisoning. We learn all this in "The Blunder Years" - and we also learn that Burns covered it all up, including failing to provide a proper burial for the corpse (seen by a young Homer, which would traumatize him) and lying to Smithers Jr. about his father's death, claiming he had been killed by a tribe of Amazonian women. No idea how that last part might have impacted the Smithers we know...