In 1985, it was a truck driver who let PCBs spill for miles along Highway 17 in northwestern Ontario. His actions focused public attention on the Ontario Tories' failure on the environment and probably was the tipping point in an election that ended 42 years of Tory rule.
In this election, it's Sam Gaultieri. This election may well swing on whether he lives or dies. Right now, it appears he'll make it.